The story follows Captain Elias Stormfield on his extremely long cosmic journey to heaven; his accidental misplacement; his short-lived interest in singing and playing the harp (generated by his preconceptions of heaven); and the obsession of souls with the "celebrities" of heaven, like Adam and Moses, who according to Twain become as distant to most people in heaven as living celebrities are on Earth. Twain uses this story to show his view that the common conception of heaven is ludicrous and points out the incongruities of such beliefs.
A lot of the description of Heaven is given by the character Sandy McWilliams, a cranberry farmer who is very experienced in the ways of heaven. Sandy gives Stormfield, a newcomer, the description in the form of a conversational question-and-answer session. The heaven described by him is similar to the conventional Christian heaven, but includes a larger version of all the locations on Earth, as well as of everywhere in the universe. All civilized life-forms from all planets travel to heaven, often through interplanetary space, and land at a particular gate, which is reserved for people from that planet. Each newcomer must thereafter give his name and planet of origin to a gatekeeper, who sends him in to heaven. Once inside, the person spends eternity living as it thinks best, usually according to its true (sometimes undiscovered) talent. According to one of the characters, a cobbler who "has the soul of a poet in him won't have to make shoes here", implying that he would instead turn to poetry and achieve perfection in it. On special occasions, a procession of the greatest people in history is formed, including Buddha, William Shakespeare, Homer, Mohammed, and several unknown people whose talents far exceeded those of the world's pivotal figures, but were never famous.
As Stormfield proceeds through heaven, he learns that the conventional image of angels as winged, white-robed figures bearing haloes, harps, and palm leaves is a mere illusion generated for the benefit of humans, who mistake "figurative language" for accurate description; that all of heaven's denizens choose their ages, thus aligning themselves with the time of life at which they were most content; that anything desired is awarded to its seeker, if it does not violate any prohibition; that the prohibitions themselves are different from those envisioned on Earth; that each of the Earthlike regions of heaven includes every human being who has ever lived in it; that families are not always together forever, because of decisions made by those who have died first; etc.