A telephone bell jangled insistently. The orderly on duty dropped his feet from the desk to the floor and lifted the receiver with a muttered curse.

“Post hospital, Aberdeen Proving Ground,” he said sleepily, rubbing his eyes.

A burst of raucous coughing answered him. Several times it ceased for an instant and a voice tried to speak, but each time a fresh spasm of deep-chested wracking coughing interrupted.

“Who is this?” demanded the now aroused orderly. “What’s the matter?”

Between intervals of coughing difficultly enunciated words reached him.

“This is--uch! uch!--Lieutenant Burroughs at the--uch!--Michaelville range. We have been--uch!--caught in a cloud of poison--uch! uch!--gas. Send an ambulance and a--uch!--surgeon at once. Better bring--uch!--gas masks.”

“At the Michaelville range, sir? How many men are down there?”

“Uch! uch! uch!--five--all help--uch! uch!--helpless. Hurry!”

“Yes, sir. I’ll start two ambulances down at once, sir.”

“Don’t forget the--uch! uch!--gas--uch!--masks.”

“No, sir; I’ll send them, sir.”

Five minutes later two ambulances rolled out of the garage and took the four-mile winding ribbon of concrete which separated the Michaelville water impact range from the main front of the Aberdeen Proving Ground. On each ambulance was a hastily awakened and partially clothed medical officer. For three miles they tore along the curving road at high speed. Without warning the leading machine slowed down. The driver of the second ambulance shoved home his brake just in time to keep from ramming the leading vehicle.

“What’s the matter?” he shouted.

As he spoke he gave a muttered curse and switched on his amber fog-light. From the marshes on either side of the road a deep blanket of fog rolled up and enveloped the vehicle, almost shutting off the road from sight. The forward ambulance began to grope its way slowly forward. The senior medical officer sniffed the fog critically and shouted to his driver.

“Stop!” he cried. “There’s something funny about this fog. Every one put on gas masks.”

He coughed slightly as he adjusted his mask. His orders were shouted to the ambulance in the rear but before the masks could be adjusted, every member of the crew was vying with the rest in the frequency and violence of the coughs which he could emit. The masks did not seem to shut out the poisonous fog which crept in between the masks and the men’s faces and seemed to take bodily possession of their lungs.

“I don’t believe we’ll ever make the last mile to Michaelville through this, Major,” cried the driver between intervals of coughing. “Hadn’t we better turn back while we can?”

“Drive on!” cried the medical officer. “We’ll keep going as long as we can. Imagine what those poor devils on the range are going through without masks of any sort.”

On through the rapidly thickening fog, the two ambulances groped their way. The road seemed interminable, but at length the flood lights of the Michaelville end of the range came dimly into view. As the vehicles stopped the two surgeons jumped to the ground and groped their way forward, stretcher bearers following them closely. Presently Major Martin stumbled over a body which lay at full length on the concrete runway between the two main buildings. He stooped and examined the man with the aid of a pocket flashlight.

“He’s alive,” he announced in muffled tones through his mask. “Take him to the ambulance and fit a mask on him.”

Three more unconscious men were carried to the ambulances before the prone form of Lieutenant Burroughs was found by the searchers. The lieutenant lay on his back not far from the telephone and directly under the glare of a huge arc-light. His eyes were open and he was conscious, but when he tried to speak, only a murmur came from his lips. There was a rattle in his chest and faint coughs tried in vain to force their way out between his stiffened lips.

“Easy, Lieutenant,” said Major Martin as he bent over him; “don’t try to talk just now. You’re all right and we’ll have a mask on you in a jiffy. That damned gas isn’t as thick right here as it is down the road a way.”

Two medical corps men lifted the lieutenant onto a stretcher and started to fit a mask over his face. He feebly raised a hand to stop them. His lips formed words which he could not enunciate, but Major Martin understood them.

“Your men?” he said between intervals of coughing. “We’ve got them all in the ambulance, I think. There were four besides yourself, weren’t there?”

The lieutenant nodded.

“Right. We have them all. Now we’ll take you back to the hospital and have you fixed up in a jiffy.”

The entire rescue crew were coughing violently as the ambulances left Michaelville. For a mile they drove through fog that was thicker than had been seen in Maryland for years. They reached the point where they had encountered the congealed moisture on the way out, but now there was no diminution of its density. The main post was less than two miles away when they burst out into a clear night and increased their speed.

As the two machines drew up in front of the post hospital, the driver of the leading ambulance swayed in his seat. Blindly he pulled on his emergency brake and then slumped forward in his seat, his breath coming in wheezing gasps. Major Martin hastily tore the mask from his face and glanced at it.

“Take him in with the rest!” he cried. “His mask must have leaked.”

As they entered the hospital, a sickening weakness overcame Major Martin. From all sides a black pall seemed to roll in on him and bits of ice seemed to form in his brain. He reeled and caught at the shoulder of a corps man who was passing. The orderly caught at him and looked for a moment at his livid face.

“Sergeant Connors!” he cried.

A technical sergeant hastened up. Major Martin forced words with difficulty through stiffening lips.

“Call Captain Murdock,” he wheezed, “and have him get Captain Williams. I’m down and probably Dr. Briscoe will be down in a few minutes. Telephone the commanding officer and tell him to quarantine the whole proving ground. Have the telephone orderly wake everyone on the post and order them to close all windows in all buildings and not to venture outside until they get fresh orders. This seems to be the same stuff they had in Belgium last December.”

As the last words came from his lips he slowly stiffened and slumped toward the ground. The sergeant and the orderly picked him up and carried him to a bed in the emergency ward. The orderly hurried away to close all of the hospital windows while Sergeant Connors took down the receiver of the telephone and began to carry out the Major’s orders.

Dr. Bird glanced at the news-paper clipping which Operative Carnes of the United States Secret Service laid on his desk. Into his eyes came a curious glitter, sure evidence that the famous scientist’s interest was aroused.

“Last December when we discussed this matter, Doctor,” said the detective, “you gave it as your opinion that Ivan Saranoff was at the bottom of it and that the same plague which devastated the Meuse Valley in Belgium would eventually make an appearance in the United States. You were right.”

Dr. Bird bounded to his feet.

“Is Saranoff back on this side of the Atlantic?” he demanded.

“Officially, he is not. Every customs inspector and immigration officer has his photograph and no report of his arrest has come in, but we know Saranoff well enough to discount negative evidence where he is concerned. Whether he is here or not, the plague is.”

“When did it appear?”

“Last night at the Aberdeen Proving Ground in Maryland. It has killed eight or ten and twice as many more are sick. The place is quarantined and a rigid censorship has been placed over the telephones, but it is only a matter of time before some press man will get the story. I have a car waiting below and a pass signed by the Secretary of War. Grab what apparatus you need and we’ll start.”

Dr. Bird pressed a button on his desk. A tall, willowy girl entered, notebook in hand. Carnes glanced with keen appreciation at her slim beauty.

“Miss Andrews,” said the doctor, “in five minutes Mr. Carnes and I will leave here for Aberdeen Proving Ground in the Government car which is waiting below. You will see that Mr. Davis is in that car and that traveling laboratory ‘Q’ is ready to follow us.”

“Yes, Doctor.”

“You remember that mysterious plague in Belgium last December, do you not?”

“Yes, Doctor.”

“I was unable to get over to Belgium, but an army surgeon and two Public Health Service men went over. You will get copies of all reports they made, including especially any reports of autopsies on bodies of victims. I want all data on file in the Public Health Service or the War Department. You will then obtain a car and follow us to Aberdeen. Arrangements will be made for your admittance to the proving ground. The Belgian plague has made its appearance in the United States.”

Swiftly the expression of the girl’s face changed. Her dark eyes glowed with an internal fire and the immobility of her face vanished as if by magic to be replaced by an expression of fierce hatred. Her lips drew back, exposing her strong white teeth and she literally spat out her words.

“That swine, Saranoff!” she hissed.

Carnes sprang to his feet.

“Why, it’s Feodrovna Androvitch!” he cried in astonishment.

In an instant the rage faded from her face and the calm, immobility which had marked it reappeared. Through the silence Dr. Bird’s voice cut like a whip.

“Miss Andrews,” he said sternly, “I thought that I had impressed on you the fact that even a momentary lapse from the character which you have assumed may easily be fatal to both of us. Unless you can learn to control your emotions, your usefulness to me is at an end.”

Although Carnes watched closely he could not detect the slightest change of expression in the girl’s face as the doctor spoke.

“I am very sorry, Doctor,” she said evenly. “We were alone and I allowed the mask to slip for an instant. It will not happen again.”

“It must not,” said the doctor curtly. “Carry out your instructions.”

“Yes, Doctor.”

She turned on her heel and left the office. Carnes looked quickly at Dr. Bird.

“Surely that is Feodrovna Androvitch, Doctor?” he asked.

“It was. It is now Thelma Andrews, my secretary. She changed her name with her appearance and politics. I have been training her since last August. This is her first official appearance, so to speak.”

“In view of her past associations, is it safe to trust her?”

“If I didn’t think so, I wouldn’t use her. She has ample reason to hate Ivan Saranoff and she knows how much mercy she has to hope for from him if he ever gets her in his clutches. We can’t play a lone hand against Saranoff forever and I know of no better place to recruit an organization than the enemy’s camp. Thelma saved our lives in Russia, you may remember.”

“But even when she was rescuing us from the clutches of Saranoff’s gang, she was an ardent communist, if I remember correctly.”

“Theoretically I believe she still favors the world revolution, but she hates Saranoff even more than she does the bourgeoisie and I believe she had come to be willing to accept capitalistic institutions for the present, at least as far as this country is concerned. At any rate, I trust her. If you have any doubts, you can have her watched for a while.”

Carnes thought for a moment and then picked up the telephone.

“I have plenty of confidence in your judgment, Doctor,” he said apologetically, “but if you don’t mind, I’ll have Haggerty trail her for a few days. It won’t do any harm.”

“Very well; and if any of the Young Labor gang should penetrate her disguise, he’d be a mighty efficient bodyguard. Do as you see fit.”

Carnes called the number of the secret service and conferred for a few moments with Bolton, the chief of the bureau. He turned to Dr. Bird with a smile of satisfaction.

“Haggerty will be on the job in a few minutes, Doctor.”

“Good enough. The five minutes I allowed are up. Let’s see how well she has performed her first task.”

As they emerged from the Bureau of Standards, Carnes glanced rapidly around. In the front seat of the secret service car which he had left sat a young man whom the detective recognized as one of Dr. Bird’s assistants. Behind the car stood a small delivery truck with two of the Bureau mechanics on the seat.

Dr. Bird nodded to the mechanics and followed Carnes into the big sedan. With a motorcycle policeman clearing a way for them, they roared across Washington and north along the Baltimore pike. Two hours and a half of driving brought them to Aberdeen and they turned down the concrete road leading to the proving ground. Two miles from the town a huge chain was stretched across the road with armed guards patrolling behind it. The car stopped and an officer stepped forward and examined the pass which Carnes presented.

“You are to go direct to headquarters, gentlemen,” he said. “Colonel Wesley is waiting for you.”

The commanding officer rose to his feet as Carnes and Dr. Bird entered his office.

“I am at your service, Dr. Bird,” he said formally. “The Chief of Ordnance has given instructions which, as I understand them, put you virtually in command of this post.” There was resentment in the colonel’s tone.

Dr. Bird smiled affably and extended his hand. The old colonel struggled with his chagrin for a moment, but few men could resist Dr. Bird when he deliberately tried to charm them. Colonel Wesley grasped the proffered hand.

“What I want most, Colonel, is your cooperation,” said the doctor suavely. “I am not competent to assume command here even if I wished to. I would like to ask a few favors but if they should prove to be contrary to your established policies, I will gladly withdraw my request.”

Colonel Wesley’s face cleared as if by magic.

“You have only to ask for anything we have, Doctor,” he said earnestly, “and it is yours. Frankly, we are at our wit’s end.”

“Thank you. I have a truck with some apparatus and three men outside. Will you have them guided to your laboratory and given what aid they need in setting their stuff up?”

“Gladly.”

“My secretary, Miss Andrews, will arrive from Washington later in the day with some information. I would like to have her passed through the guards and brought directly to me wherever I am. You have the place well guarded, have you not?”

“As well as I can with my small force. All roads are patrolled by motorcycles; four launches are on the waterfront, and there are seven planes aloft.”

“That is splendid. Now can you tell me just what happened last night?”

“Captain Murdock, the acting surgeon, can do that better than I can, Doctor. He is at the hospital but I’ll have him up here in a few minutes.”

“With your permission, we’ll go to the hospital and talk to him there. I want to examine the patients in any event.”

“Certainly, Doctor. I will remain at my office until I am sure that I can give you no further assistance.”

With a word of thanks, Dr. Bird left, and, accompanied by Carnes, made his way to the hospital. Captain Murdock was frankly relieved to greet the famous Bureau of Standards scientist and readily gave him the information he desired.

“The first intimation we had of trouble was when Lieutenant Burroughs telephoned from the water impact range where they were doing night firing last night at about four A.M. Two ambulances went down and brought him and his four men back, all of them stricken with what I take to be an extremely rapidly developing form of lobar pneumonia. All of the men who went down were stricken with the same disease, two of them as soon as they got back. So far we have had eight deaths among these men and all of the rest, except Lieutenant Burroughs, are apt to go at any moment.

“The trouble seemed to come from a cloud of some dense heavy gas which rolled in from the marsh. On the advice of Major Martin, every door and window in the post was kept closed until morning. The gas never reached the upper part of the post but it reached the stables. Eleven horses and mules are dead and all of the rest are stricken. The stable detachment either failed to close their barracks tightly or else the gas went in through cracks for seven out of the nine are here in the hospital, although none of them are very seriously ill. As soon as the sun came up, the gas seemed to disappear.”

“Let me see the men who are sick.”

Captain Murdock led the way into the ward. Dr. Bird went from man to man, examining charts and asking questions of the nurses and medical corps men on duty. When he had gone the rounds of the ward he entered the morgue and carefully examined the bodies of the men who lay there.

“Have you performed any autopsies?” he asked.

“Not yet.”

“Have you the authority?”

“On the approval of the commanding officer.”

“Please secure that approval at once. Have all lights taken out of the operating room and the windows shaded. I want to work under red light. We must examine the lungs of these men at once. With all due respect to your medical knowledge, Captain, I am not convinced that these men died of pneumonia.”

“Neither am I, Doctor, but that is the best guess I could make. I’ll have things fixed up for you right away.”

Dr. Bird stepped to the telephone and called the laboratory. When, in half an hour, Captain Murdock announced that he was ready to proceed, Davis had arrived with an ultra-microscope and other apparatus which the doctor had telephoned for.

“Did you arrange about the horses, Davis?” asked Dr. Bird.

“Yes, sir. They will be up here as soon as the trucks can bring them.”

“Good enough. We’ll start operating.”

An hour later, Dr. Bird straightened up and faced the puzzled medical officer.

“Captain,” he said, “your diagnosis is faulty. With one possible exception, the lungs of these men are free from pneumonicocci. On the other hand there is a peculiar aspect of the tissues as though a very powerful antiseptic solution had been applied to them.”

“Hardly an antiseptic, Doctor; wouldn’t you say, rather, a cauterizing agent.”

Dr. Bird bent again over the ultra-microscope.

“Are you familiar with the work done by Bancroft and Richter at Cornell University last November and December?” he asked.

“No, I can’t say that I am.”

“They were working under a Heckscher Foundation grant studying just how antiseptic solutions destroy bacteria. It has always been held that some chemical change went on, but this theory they disproved. It is a process of absorption. If enough of the chemical adheres to the living bacterium, the living protoplasm thickens and irreversibly coagulates. It resembles a boiling without heat. I have seen some of their slides and the appearance is exactly what I see in this tissue.”

Captain Murdock bent over the microscope with a new respect for Dr. Bird in his face.

“I agree with you, Doctor,” he said. “This tissue certainly looks as though it had been boiled. It is certainly coagulated, as I can plainly see now that you point it out to me. You believe, then, that it is a simple case of gassing?”

“If so, it was done by no known gas. I have studied at Edgewood Arsenal, and I am familiar with all of the work done by the Chemical Warfare Service in gases. No known gas will produce exactly this appearance. It is something new. Carnes, have those horses been brought up yet?”

“I’ll see, Doctor.”

“If they are, bring one here.”

In a few moments the body of a dead horse was dragged into the operating room and Dr. Bird attacked it with a rib saw. He soon laid the lungs open and dragged them from the body. He cut down the middle of one of the organs and shaved off a thin slice which he placed under the lens of a powerful binocular microscope.

“Hello, what the dickens is this?” he exclaimed.

With a scalpel and a delicate pair of tweezers he carefully separated from the lung tissue a tiny speck of crystalline substance which glittered under the red light in the operating room. He carefully transferred it to a glass slide and put it under a microscope with a higher magnification.

“Rhombohedral regular,” he mused as he examined it. “Colorless, friable, and cleaving in irregular planes. What in thunder can it be? Have you ever seen anything like this in a lung, Murdock?”

The medical officer bent over the microscope for a long time before he shook his head with a puzzled air.

“I never have,” he admitted.

“Then that’s probably what we’re looking for. Start slicing every lung in this place and look for those crystals. Save them and put them in this watch glass. If we can get enough of them, we may be able to learn something. Carnes, get the rest of those horses in here and open them up.”

Two hours of careful work netted them a tiny pile of the peculiar crystals. Some had come from the lungs of the dead animals and some few from the lungs of the dead soldiers. Dr. Bird placed the crystals in a glass bottle which he covered with layer after layer of black paper.

“Get me more of those crystals if you can find them, Captain Murdock,” he said, “and in any case, leave the bodies here for further study. Davis and I will go to the laboratory and try to find out what they are. Carnes, hasn’t Miss Andrews showed up yet?”

“No, Doctor.”

“Locate her on the telephone if you can and tell her not to bother about anything except the autopsy reports and to get them here as quickly as possible. Let me know when you have that done.”

In a dark room of the photographic laboratory, Dr. Bird removed the black wrappings from the bottle. He dropped a few of the crystals in a test tube and added distilled water. The water assumed a pink tinge as the blood with which the crystals were covered dissolved, but the crystals themselves did not change. They rose and floated on the surface of the water.

“Insoluble in water, Davis,” commented the doctor. “Better wash the lot and then we’ll get after the ultimate analysis. Whether we’ll be able to make a proximate is doubtful in view of the small amount of sample we have. It’s dollars to doughnuts that it’s some carbon compound.”

He heated a few of the washed crystals in a watch glass. Suddenly there was a sharp crack and the material disappeared. Dr. Bird thrust his nose toward the glass and sniffed carefully.

“The dickens!” he muttered. “Davis, have I got a cold or do you smell garlic?”

“Faintly, Doctor.”

“I have a hunch. Fill a gasometer with purified argon and we’ll introduce a few of these crystals and explode them. If I’m right--”

Half an hour later he straightened up and examined the tube of the gas analysis apparatus with which he was working. The level of the gas showed it to be of the original volume but the liquid under the argon was stained a light brown.

“It’s impossible, Davis,” cried the doctor, “but nevertheless, it’s true. Expose some of those crystals to strong sunlight and see what happens.”

The crystals rapidly disappeared as the light from a sun-ray arc fell on them.

“It’s true, Davis,” cried the doctor, positive awe in his voice. “Keep this strictly under your hat for the present. Now that you know what we’re up against, fix up a couple of masks and air-collecting apparatus. That stuff will show up again in the swamp to-night and I am going down there to collect some samples. I’ll telephone the hospital now.”

As Dr. Bird emerged from the dark room, Carnes hurried up with a worried expression.

“The devil’s to pay, Doctor,” was his greeting.

“All right, stall him off for a minute while I telephone the hospital. I think I can save some of those poor fellows up there.”

Carnes paced the floor in anxiety while Dr. Bird got Captain Murdock on the telephone.

“Bird talking, Murdock,” he said crisply. “How much deep therapy X-ray apparatus have you got up there? ... Too bad ... Well, at least you can give every patient a four-minute dose of maximum intensity and repeat in an hour or so. Keep them under sun-ray arcs as much as you can. Be ready for a fresh attack of the same epidemic to-night. As fast as the patients come in, give them a five-minute dose of X-rays and then sun-rays. Do you understand? ... All right, then.”

“Just a moment more, Carnes,” he went on as he called the office of the commanding officer. “Colonel Wesley, this is Dr. Bird. I think that I have some light on your problem. You must anticipate another more virulent attack than you had last night, probably as soon as the sun goes down. Will you arrange to have everyone removed from the swamp area before that time? Never mind trying to guard the place; you’ll just lose more lives if you do. Warn everyone to keep inside the buildings with all doors and windows closed tight. Get all the women and children and everyone else who isn’t needed here off the post before dark. Send them to Aberdeen or Baltimore or anywhere ... No, sir, the sick had better not be moved. I think they will be safer in the hospital than they would be elsewhere ... Yes, sir, that’s all. Thank you.”

Dr. Bird turned to the waiting Carnes.

“Did you locate Miss Andrews?” he asked.

“No, I didn’t and that is what I want to talk to you about. I just started to telephone when a hurry call came through from Washington for me and I took it. It was Haggerty on the wire. He followed your precious secretary from the Bureau of Standards over to the Public Health Office and waited for her to come out. She stayed in the building for about an hour and brought a bundle of papers with her when she returned. She walked toward the State, War and Navy Building and Haggerty followed.

“On Pennsylvania Avenue, she was stopped by two men whom Haggerty describes as dark, swarthy, bearded Europeans of some sort. He tried to overhear their conversation but it was in a language which he did not recognize. He got only one word. The girl called one of them ‘Denberg.’”

“Denberg!” cried the doctor, “Why, he’s one of the Young Labor crowd, but he’s in Atlanta.”

“He was, Doctor, but I telephoned Atlanta, and found that he had been released last month. After several minutes of talk the two men and your secretary went off together in perfect amity with Haggerty following. The trio got into a waiting car and Haggerty trailed them in a taxi. They drove around town rather aimlessly for some time and then left the car and walked. Haggerty was afraid he would lose them in the crowd so he closed in on them. He doesn’t know what happened except that he felt a sudden stab in his arm and everything went black. He recovered in the police station twenty minutes later but the birds had flown.”

“The devil!” cried Dr. Bird, consternation in his voice. “Of course, it’s easy to see what happened. They spotted him and a confederate slipped a hypo into his arm. What worries me is the fact that they’ve got Thelma.”

“I hope they kill her,” snapped Carnes vindictively. “She was never kidnapped in broad daylight. Haggerty says she went with them quite willingly and talked and laughed with them. She has deserted, if she wasn’t simply acting as a spy from the first. I didn’t trust her at all.”

“I hate to admit that my judgment is that rotten, Carnes, but the evidence certainly points that way. At that, I think I’ll reserve final judgment until later. Now, in view of what you have learned, I have a job for you.”

“It’s about time, Doctor. I have been rather useless with all the high-powered science that has been flying around here.”

“Well, you’ll be in your element now. We know that Denberg is loose and their capture of Thelma is no coincidence. I was pretty sure that Saranoff and his gang were at the bottom of this; now I am certain. They must have introduced something onto the marshes last night which caused the trouble. They could not have come overland very well, for the place is too well patrolled. Had they come by air, they would have attracted attention, even had they used a Bird silencer on their motor, for they couldn’t muffle their propeller, especially on a takeoff, and there are plenty of men here who would have recognized it. You might check up on that, but I am confident that they came by water. Launches and boats are continually passing up and down the Chesapeake and its tributaries and one more could easily have escaped notice. The Bush River is at the far end of the Michaelville range and it is navigable for craft of light draft at high tide. Find out whether any strange craft were seen in the vicinity of the proving ground last night. If you draw a blank, go to Perryville and Havre de Grace and see what you can find out there. I have a hunch that their base is more likely to be up the Susquehanna than down toward the coast. Above all, Carnes, don’t approach the proving ground by water to-night and don’t get near the mouth of the Bush River.”