Malachi Constant, a young earth man in the 22nd century, is the richest man on earth, money inherited from his estranged father. His father made his money from a series of lucky (or were they?) stock market investments, and this lucky streak follows Constant into an indulgent playboy lifestyle that leads many to wonder how he deserves it. Yet, Constants life falls to pieces when he meets a most unique man, Winston Niles Rumfoord. Rumfoord (and his trusty dog) were the first to buy a private space ship, and on the maiden voyage to space were caught in a temporal flux which causes them to materialize and vanish in his home mansion periodically, as well as on Mars, and Titan, one of Saturn's moons. Rumfoord invites Constant to a materialization, where he claims that he has had a glimpse of his entire life from birth to death. Before he disappears, Rumfoord, in a Sophoclean oracle like manner, reveals parts of Constants future to Constant- Constant will have a child with Mrs. Rumfoord on Mars, and then he will travel to Mercury, back to Earth, and finally to Titan, where he will settle with his wife and son. He also says his son will hold a piece of metal that is of incredible importance. Constant does not believe him, and Mrs. Rumfoord, who has also heard this prophecy, is repulsed by the idea, and also believe she can change here fate.
However, Constant soon loses his money in bad investments, and finds out one of his pharmaceutical products has caused widespread infertility among those who bought it. The night he loses his money he is invited by two Martian recruiters to lead an army of humans who are building up forces on a hidden Mars base. Constant takes the deal, and escapes the lawsuits and poverty on Earth.
The story now begins to follow the character Unk, who is a Martian recruit, who has had his memories wiped away by the Martian army. Everyone in the army is under mind control, and Unk is directed to execute his only friend in the world, only he does not recognize him, after having his memory recently wiped. Afterwards, he finds a note left by himself revealing he has a family, so he escapes from the camp and tries to rescue his wife (Mrs. Rumfoord, who was kidnapped by the Martian recruiters), and his son Chronos. He fails.
The assault on Earth begins, with thousands of Martian troops, but nearly the entire invasion is destroyed en route by nuclear missiles. Mrs. Rumfoord and Chronos survive and land on earth, where they try to make a new living, but having no memory of the past. Unk, who is Constant, and another Martian end up on Mercury, after their ship was reprogrammed by Rumfoord. On Mercury, they discover wonderful creatures in a deep cave that live on music. Eventually Unk figures out how to navigate the ship back to Earth, and his Martian "friend" opts to stay behind with the creatures, which he feels obligated to take care of, after causing so much pain for other earlier in his life.
Back on Earth, Constant is met as a prophet, his arrival being prophesied by Rumfoord, who has become an almost godlike symbol on earth, power which he has used to unite the Earth, catalyzed by the Earths united fight against the Martians, which Rumfoord was behind, in a new religion. This religion is based on a god who does not care about humans. Everyone handicaps themselves so they can all be equal. The central belief is that everyone's life is a series of accidents. Rumfoord tells his followers about Constant's life of indulgence and waste, perpetuated by luck, and everyone voices their hatred for Constant. Hounded by humanities hatred for him, Constant boards a spacecraft bound to Titan, where he will live out his days in banishment. Mrs. Rumfoord and Chronos join him, having no place on Earth either.
On Titan, Constant meets a robot named Salo, who crash landed on Titan while on a mission to deliver a message to the other side of the Galaxy. The robot is waiting for a replacement part to fix his spaceship, this spaceship being the model for which all of the Martian Invasion ships were based. Chronos has a bit of scrap metal he picked up on Mars which is his good luck charm. This piece of metal turns out to be the replacement part for Salo's space ship, and it is revealed that the entire human existence was engineered by Salo's people in order to create this one piece of metal, and now that the task is done, humanity is either finally under will, or is meaningless. Salo, on discovering this, decides to read the message (having previously forbidden to) he is supposed to deliver, the delivery of which was so important that an entire race was engineered. It says only "Greetings". Salo goes mad at the pointlessness of existence and tears himself apart.
Rumfoord's existence is ripped away from the solar system after a solar storm, but not before his dog is torn away form him, dooming him to roam a cold and unfamiliar universe alone.
The family grows old on Titan, Constant learns to love Mrs. Rumfoord. Constant puts Salo back together, and Salo decided to finish his journey. He drops Constant back on Earth, where constant dies in the snow waiting for a bus, hallucinating that his best friend is beckoning him into heaven.