The novel is set in the future, between World War II and the “Third Great Depression,” and opens in Newport, Rhode Island. Malachi Constant, the richest man in the U.S., has arrived to witness the “materialization” of Winston Niles Rumfoord and Winston’s dog, Kazak. Constant was invited to the event, which is taking place on the Rumfoord Estate, by Mr. Rumfoord’s wife, Beatrice. Mr. and Mrs. Rumfoord are extremely rich, with the highest social status in the country. Nine years ago, Mr. Rumfoord drove his spaceship into a chrono-synclastic infundibulum, which landed him in a kind of time warp, allowing him to see the past and future. It also means that he materializes on Earth and other planets at regular intervals.
Constant’s encounter with Rumfoord leaves him feeling self-conscious, as he is struck by the realization that Rumfoord is “superior” to him. Rumfoord prophesizes that Constant will end up being “bred” like an animal with Beatrice on Mars, and that they will have a son together. He also says that Constant will travel to Mars, Mercury, and back to Earth before ending up on Titan. Constant is untroubled by this prediction at first, but soon becomes terrified of the thought that he might die on Titan. He does everything in his power to stop the prophecy from coming true, including throwing a party that last for 56 days, during which he gets so intoxicated he gives away oil wells to all the guests and marries a blonde woman he doesn’t know. When he regains consciousness, he learns that his company, Magnum Opus, has gone bankrupt.
Magnum Opus was originally founded by Malachi’s father, Noel, when Noel was 39. A “business failure” with nothing going for him, Noel decided to become a speculator and chose companies to invest based on the first letters of the Old Testament of the Bible. The strategy turned out to be an enormous success, although Noel never understood why. Noel spent his life living at the Wilburhampton Hotel, where he paid a maid, Florence Whitehill, to have sex with him once every 10 days. As a result of these encounters she becomes pregnant with a son, Malachi.
Noel and Malachi meet only once, on Malachi’s 21st birthday, when Noel informs his son that he will be handing over the business to him. It is an awkward encounter, and five years later, Noel dies. Back in the present, having just learned that Magnum Opus is bankrupt, Malachi goes to the Wilburhampton to read a letter his father left for him in case his luck ever turned. After reading the letter, Malachi is offered a position in the Martian Army by two recruiters, Helmholtz and Wiley. He accepts. Beatrice is also conscripted, although she doesn’t realize this is happening at the time.
On Mars, Malachi’s memory is erased and he is given a new identity, Unk. An antenna is implanted in his head that gives him instructions and causes him pain any time he does something of which the army doesn’t approve. Now, he is forced to execute a man who the reader later learns is Unk’s best friend, Stony Stevenson. However, Unk doesn’t recognize Stony because his memories have been erased over and over inside the army hospital.
Back in his barrack, Unk speaks to another soldier, Boaz, who is secretly one of the “real commanders” of the army. These commanders have special rights and privileges, and do not have antennae. They hide among the ordinary members of the army in order to prevent rebellion. While the rest of the soldiers are engaged in a game of German batball, Unk finds a letter addressed to him which contains an extraordinary amount of information about the army. It suggests that Unk and Stony have been rebelling, and encourages Unk to disobey his antenna, even though it’s painful to do so. It informs Unk about his “mate,” Bee, and son, Chrono, who live in the Martian city of Phoebe. To Unk’s great surprise, the letter is signed by himself.
As the war between Mars and Earth begins, Unk decides to become the only deserter in the history of the Martian Army and escape along with Bee, Chrono, and Stony. He manages to flee to Phoebe and finds 8-year-old Chrono playing a game of German batball at his school. Taking Chrono aside, Unk tries to tell him that he is his father and wants to rescue him, but Chrono is not interested. When Unk approaches Bee (who teaches therapeutic breathing at the Schliemann Breathing School for Recruits) she is similarly resistant to the idea of fleeing. He ends up being recaptured by Rumfoord, and wakes up aboard Rumfoord’s ship.
Rumfoord is “commander-in-chief of everything Martian.” He tells Unk about how Chrono was conceived on a spaceship between Earth and Mars (it is implied that this may have been a result of Unk raping Beatrice). The war between Mars and Earth leads to the utter slaughter of the Martian Army and the total destruction of Martian civilization. The war was designed by Rumfoord but technologically engineered by Salo, an alien messenger from the planet Tralfamadore who has been stranded on Titan for 200,000 years after his spaceship broke down.
On Earth, Rumfoord founds a new religion, the Church of God the Utterly Indifferent. He sends Unk and Boaz to Mercury on an autopiloted ship, where they remain stuck for three years. Boaz has a breakdown and becomes obsessed with harmoniums, the strange, coral-like aliens that live in Mercury’s caves. When Unk finally finds a way to escape Mercury, Boaz decides to stay and live with the harmoniums forever.
Unk (Constant) arrives back on Earth, where his appearance has been foretold by the Church of God the Utterly Indifferent. The church calls him the Space Wanderer. When the crowds of people gathered to greet him ask what happened to him, he explains that he was “a victim of a series of accidents […] as are we all.” This is met with rapturous applause. The Space Wanderer, Bee, and Chrono are all taken to the Rumfoord Estate in Newport. It is revealed that Malachi Constant is a demonized figure within the Church, made to represent everything that the Church opposes.
Rumfoord delivers a speech in which he reveals that the Space Wanderer and Constant are the same person, then sentences Constant, Bee, and Chrono to “peaceful exile” on Titan. There, Salo enthusiastically greets Rumfoord, who is cruel to him in return. Rumfoord has become ill due to encountering sunspots while in the chrono-synclastic infundibulum—he will soon die. It’s revealed that Salo was stranded while delivering a message across the universe; he doesn’t know the message’s contents, and because, like all Tralfamadorians, he is a machine, he has never tried to find out. It is revealed that the whole history of human civilization was designed by the Tralfamadorians in order to help get the missing part Salo needs for his spaceship. Rumfoord demands to know the contents of the message Salo is carrying as a dying wish. Salo hesitates, and by the time he agrees, Rumfoord is dead. Distraught, Salo commits suicide by disassembling himself. Chrono drops the missing part for Salo’s spaceship—which he has been carrying around as a “good-luck piece”—among Salo’s scattered parts.
Constant and Beatrice both live to the age of 74. In the meantime, Chrono joins the birds of Titan, living among them and learning their language. Beatrice dies first, and Constant, heartbroken, buries her. Salo offers him a ride to Earth, and Constant accepts, requesting to be dropped off in Indianapolis. En route, Salo hypnotizes Constant and plants a pleasant illusion in his mind. He drops Constant in Indianapolis by a bus stop, and Constant dies in the snow while waiting for the delayed bus. As Constant dies, he experiences the illusion Salo implanted in him—a dream that Stony is bringing him to paradise, where Beatrice is waiting.
