In 1959, eight people visit the Belmont Bevatron, a large particle accelerator. The tour group is made up of a fairly diverse group of people. Jack Hamilton has been terminated from his job at the California Maintenance Labs because it is suspected that his wife is a Communist. In particular, McCarthy-like security chief Charlie McFeyffe is obsessed with weeding out left-wing sympathizers. Arthur Sylvester, a senior, is a believer in obscure methods of cosmology, walks the tour with Joan Reiss, who is interested in the facility but constantly neurotic and paranoid. Mother and son Edith and David Pritchet round out the group of tourists, and they are led around the facility by a physicist by the name of Bill Laws.
The Bevatron malfunctions and the members of the tour group are all injured in varying degrees by a walkway that collapses on top of them. They are also negatively affected by the large amounts of radiation that they are exposed to. Momentarily rendered barely conscious, or unconscious, they awaken to find themselves in a strange world where the miraculous is common, and where there are daily examples of miracles and curses. Jack Hamilton and Charlie McFeyffe ascend to Heaven where they are able to see God. Heaven then becomes the brain of Arthur Sylvester, and from inside his mind they knock him out again in the hopes that this will reverse whatever took place that sent them to this alternative reality. There hopes are dashed when they realize that they are moving from one alternative universe to another.
The next reality for the men is a Victorian version of the world presided over by Edith Pritchett; judgmental and censorious on her best day, in this universe she has abolished everything that she considers unsuitable which is almost everything that anyone else has ever derived enjoyment from. From here, they travel onto the next universe which is a hyperbolic interpretation of the paranoid thoughts of Joan Reiss. The final stop is a Marxist vision of America where Charles McFeyffe is discovered to be the Communist agent, and it is also discovered that he falsely accused Hamilton's wife of left-wing sympathies in order to mask his own.
McFeyffe is knocked unconscious by the rest of the group who hope that this will finally allow them to return to their real world. Believing themselves to be "home", Jack and Bill Laws build a stereophonic technology company.Although the group known McFeyffe is a Communist they are unable to prove it and so the allegations against him are dismissed.
The question remains at the end of the novel: are the characters living in their own reality, or the alternative reality of somebody else?
