Philip K. Dick's 4th novel, written in 1957. Even at this early stage in his development as a writer PKD starts to explore many of the themes that are ever present in his later work: reality distortion, neurosis, paranoia, schizophrenia, civil rights, and individualism. These are quite unconventional and mature themes for science fiction, especially for that period in America.

WARNING: Plot spoilers follow.

A group of people assembled mostly by chance are involved in an accident which plunges them in to alternate worlds which behave according to the world-views of sucessive individuals within that group. Every time they seem to escape back in to the "real" world they actually travel to progressively more dangerous worlds as they explore the neurosis and psychosis of the other characters. The reader is made very sensitive towards the likely variations in the perception of reality among other people, but also quite empathetic towards their common humanity. Even at their worst people are more to be pitied than despised.