As the narrator Grabowski rides across the railway bridge that was part of his regular three-day-a-week routine ten years before the war, he recalls his earlier life. At that time he worked as a messenger for the Reich Gun Dog and Retriever Association. He had little education, knew nothing about dogs, and had only to transport urgent correspondence, money, and a large manila folder of "Pending Cases" between the Königstadt head office and the Gründerheim branch office. The trip required crossing the Rhine River at one of its widest points. Although he crossed on a wide four-track railway bridge, the crossing always frightened him. With nothing able to convince him that the bridge was safe, he fixated on the first house on solid ground on the far side, a two-story house just before the town of Kahlenkatten. On his regular trips to Gründerheim on Mondays, Wednesdays, and Saturdays, he always saw the same woman scrubbing the floor by the windows on his left side. When it was not raining, a young girl would be sitting on the front steps holding a large clean doll, frowning at the train. On his return trips from Gründerheim, he saw the woman washing the windows in the rear of the house, always in a certain order. Gradually Grabowski became obsessed wondering which windows the woman washed on Tuesdays, Thursdays, and Fridays, when he did not ride past her house. He drew up a cleaning timetable for the week, and from what he had observed on three mornings, tried to fill in the other three mornings and all the afternoons. So preoccupied was he with the house-cleaning schedule that on one occasion he forgot to deliver the "Pending Cases" folder and was duly admonished.
At first the district manager threatened to fire him, then suddenly became human and instead gave him a day off to sort out his troubles. On that day, a Thursday, Grabowski rode the usual train route four times in each direction, from 8:00 A.M. to 6:00 P.M., and worked out the woman’s whole Thursday timetable, which included cleaning the front steps. On his last trip, he also saw a stooped man humbly digging in the garden, watched by the little girl. The remainder of the story takes place after the war. Passenger cars have been replaced by boxcars, the four-track bridge has been reduced to a one-track temporary bridge that wobbles dangerously. Whereas previously only the narrator feared the crossing, now everyone is afraid, and car after car of passengers falls silent as they leave firm ground and head precariously out over the Rhine. Only after his car has safely made the crossing does Grabowski suddenly realize that he is on his old familiar route. He wonders if the house is still standing. It is, and is still very clean. Gripped by an indefinable emotion as thoughts of the past rage within him, Grabowski sees a woman washing the steps of the house. It is not the mother now, but the daughter, and it is in fact Thursday.