Len Mattern is a space merchant, seasoned from decades of meandering from star to star in a tramp freighter. His obsession is the high-class prostitute, Lyddy, and Len has spent his entire adult life amassing sufficient wealth to wed her, which he does at the story's beginning. The rest of the tale is told mostly in flashback.
Lieutenant Commander Frank Jacklin is blown up in a thorium bomb explosion while on the battleship Alaska. He awakens in the body of Winnie Tompkins who had perpetrated the explosion. As Tompkins, he learns of a plot by German agents to poison Franklin D. Roosevelt and he tries to warn the authorities. He continues to become involved in intrigue until another accident restores Tompkins to his body, leaving Jacklin in the body of a dog.
Harry Scott is being pursued by some things. They're not human. They're not-men. A door bangs. Footsteps tread heavy. A phone ringing. Can Doctor Webber help poor, delusional Harry?
Hale Oakham heads into the mysterious jungle to find the mysterious Sir Basil Addington and his laboratory where he has supposedly discovered amazing secrets about life, including ones which enable him to produce monsters and to change the physical characteristics of humans.
