Far from Earth, on a ship carrying the 13th and 14th generations of descendants from the original crew, life is short. You are born, learn the tasks needed to keep the ship running, help breed and train the next crew - and your death is ordered by the computer in charge.
Gregson, chief of the psych-police, makes sure the computer's death-sentences are carried out quickly and painlessly. His duty is a sacred trust. He knows the intricacies of the system, how it works . . . and how it can be subverted.
He is growing old. Rebellious.
He also knows his name will soon come up in the computer for elimination.
And he has no intention of carrying out his own death-sentence!