Monette, a middle-aged traveling book salesman (his first name is never given), goes to confession. When the priest asks him what sin he has committed, Monette admits that while he believes he has sinned in some way, he is not entirely sure exactly what he is guilty of. He then explains the events of the preceding days.
While on the road, Monette picked up a hitchhiker, carrying a sign sign proclaiming him to be both deaf and mute. Once in the car, the hitchhiker seemingly falls asleep. Since Monette believes that the man cannot hear him, he decides to vent his problems to him.
Some time before the story, Monette discovered that his wife had been carrying on an affair for two years with a teacher in the school district she worked for. Despite their ages (he was 60, she was 54), their activities included binge drinking, fetishism, and compulsive gambling. She was employed by the district in an administrative position, and had access to large amounts of money, which she soon started to embezzle from her employer in order to buy various erotic underwear and sex toys. As her debt grew, she and her lover hoped to pay the money back by winning the lottery, only to embezzle more than a hundred thousand dollars without earning any to replace it. She revealed this all to Monette and to his disbelief tried to blame him for it, claiming his lack of interest drove her to it.
Continuing to speak to the apparently sleeping hitchhiker, Monette expressed his anger at her irresponsibility and ill-concern as to how this debt would ultimately affect their college student daughter (who is unaware of her mother's sordid antics). Stopping at a rest stop, Monette went to the bathroom. When he returned, he found the hitchhiker gone, having taken nothing of value save for Monette's medallion of St. Christopher. Monette thought nothing of this until two days later when the police called to inform him that his wife and her lover were beaten to death in a motel room.
The priest, horrified and intrigued by the story, asks of the aftermath. Monette relates how he believes the hitchhiker was in fact not deaf and heard the whole story. Monette had mentioned the name of the motel that his wife and her lover were living at, which would have made finding them a simple matter. He also presumably determined Monette's address by looking at the registration in the car, since Monette later found his medallion lying on his desk with a note (presumably from the hitchhiker) thanking him for the ride. Monette (truthfully) denies having intentionally set the hitchhiker up to kill his wife, but admits he is relieved about her death: he has an alibi, and his wife's life insurance will be sufficient to repay the money she embezzled. The priest admonishes his relief and tells him to do ten Our Fathers and Hail Marys. Before leaving, Monette asks about the possibility of God putting the hitchhiker in his car. The priest's first impulse is to say yes, but he outwardly admonishes Monette for blasphemy and adds ten Our Fathers to his atonement. He then asks Monette if he genuinely wants the killer to be caught. Monette insists that he does, but it perhaps not entirely sure: on his way home, he adds a few extra Our Fathers and Hail Marys.