The story opens with the unnamed first-person narrator musing that at one time he had believed that his travels in outer space could not alter his faith in God. The reader learns that he is a Jesuit as well as an astrophysicist. He is aboard a starship returning from a scientific mission three thousand light-years from Earth. Something he learned on this mission, as yet unknown to the rest of the scientists and crew, has caused him to question his faith. He reflects regretfully that the data gathered on the mission will soon make the cause of his own doubt-"this ultimate irony" — known to everyone.

The narrator reflects on the "private, good-natured, but fundamentally serious war" that the largely irreligious crew has waged with him during the long mission. He thinks particularly of the ship's doctor, Dr. Chandler, who sometimes professes himself willing to...