Gregor Samsa, a traveling salesman, wakes up one morning and discovers that he's transformed into a giant cockroach (or some similar oversized, insect-like vermin). He realizes he's missed his train, and gets acquainted with his awkward new body as he worries about his stressful salesman job. His mother, father, and sister Grete realize something's amiss and knock at his door, but he finds he can't produce human speech and also can't open the door. His boss, the Chief Clerk, arrives, and scolds him for his tardiness and strange behavior, even suggesting that his job might be in danger. Gregor finally opens his door with difficulty and gives the Chief Clerk a long speech about his dutifulness to his job. But no one understands the speech, his family is shocked at his appearance, and the Chief Clerk runs away. Gregor injures himself when he squeezes back through the doorway into his bedroom.
Gregor finds that Grete has brought him some fresh food, which doesn't appeal to him. Gregor resolves to help his family deal with the trouble he's causing them with his metamorphosis. The following morning Grete brings Gregor rotting food, and he eats hungrily. Gregor overhears the family talking about their finances, and determining that they will have to go back to work, now that he can no longer provide for them. Gregor feels upset and sorry that he can't support them anymore. About a month passes, with Grete taking care of Gregor less and less attentively. One day Grete sees Gregor out of his hiding place and is disturbed. Another month passes, then Gregor's mother wants to come help Grete and support Gregor. Grete and the mother plan to move Gregor's old furniture out so he can crawl more freely, but Gregor decides that he wants to keep his furniture, which links him to his humanity. He climbs the wall and places himself over his print of the lady with the muff, which shocks his mother when she returns to the room, causing her to faint. Gregor's father returns home and finds Gregor panicking in the dining room. Gregor's father pelts Gregor with apples, one of which severely injures him.
Another month passes while Gregor recovers from his injury. His family members are exhausted from working, and Gregor feels neglected. The family takes on three lodgers for additional income, and Gregor feels even more ignored. One night Grete plays her violin for the lodgers. Though the lodgers seem bored, Gregor is profoundly affected, and crawls out of his room, enjoying the beautiful music and optimistic that he'll be able to help his family and become close to Grete again. The lodgers notice Gregor with disgust, and decide that they'll leave and not even pay for the time they'd stayed so far. Grete tells her mother and father that the cockroach, which she can't even believe is Gregor, has ruined their lives. Gregor feebly returns to his room, thinks of his family with love, and dies. The charwoman who cleans the house discovers his body the next morning. Grete, her mother and father decide to take off work. They go to the countryside by tram, and talk happily about future plans, and finding a new apartment. Gregor's mother and father realize that it is time to find a husband for Grete.