At the start of Twain's "The Invalid's Story," the narrator describes himself as looking and feeling older than his actual age. He mentions that he was once much healthier and blames his decline on the peculiar events of one winter night when he traveled 200 miles with a box of guns.

The narrator recounts arriving at his home in Cleveland, Ohio, two years prior, only to learn about the recent death of his friend, John B. Hackett. Respecting Hackett's final wishes, the narrator heads to the train station to transport Hackett's body back to his parents in Bethlehem, Wisconsin.

At the train station, the narrator finds a white-pine box that matches the description of the coffin. He attaches an address card from Hackett's father, Deacon Levi Hackett, to the box and has it loaded into the express car—a faster and safer, yet more expensive, method for transporting packages by train than normal freight cars.

The narrator leaves to buy food and cigars. Upon returning to the area where he initially found the white-pine box, he notices a young man attaching an address card to an identical box.

The narrator checks to ensure his white-pine box is still in the express car, which it is. At this point, the narrator reveals to the reader that the boxes have been mislabeled. The first box, the one in the express car that the narrator believes contains his friend's corpse, actually holds a box of guns destined for Peoria, Illinois. Meanwhile, the second box, which the young man believes contains the guns, actually holds John Hackett's body.

However, the narrator is unaware of this mix-up during the train trip. He settles into the express car with the expressman—the man hired by the express company to oversee the express packages—for the long, 200-mile journey. Just before the train departs, a stranger briefly enters the express car and places a package of ripe Limburger cheese on top of the white-pine box. Neither the narrator nor the expressman, named Thompson, realize that the "coffin" contains guns, nor do they know that the package placed on top contains ripe cheese. The narrator informs the reader of these facts, although he was unaware of them during the train ride.

As Thompson begins to seal the car against the raging winter storm outside to keep himself and the narrator warm, the ripe cheese also starts to heat up and emit a strong odor. The narrator is the first to notice it and mistakenly thinks it is the smell of Hackett's corpse decomposing. Thompson lights a fire to provide warmth, which only intensifies the cheese's stench. Initially cheerful and singing happy songs, Thompson eventually notices the foul smell and stops singing.

Thompson also assumes the odor is coming from a decaying corpse, leading him and the narrator to discuss it. Thompson remarks on the corpse's smell and mentions he has previously transported people who were not truly dead but merely in a trance. However, he asserts that the narrator's friend is definitely dead, judging by the stench.

To escape the smell, Thompson breaks one of the express car's window panes and sticks his nose outside for fresh air. He and the narrator take turns breathing at the window. Thompson then asks how long the narrator's friend has been dead. He is skeptical of the narrator's claim that Hackett died recently, arguing that a corpse could not rot and produce such a strong odor in just a few days. Thompson chastises the narrator, saying Hackett's body should have been buried long ago. Meanwhile, the cheese's smell becomes so unbearable that the narrator...