Part I:

One day, Gregor Samsa, a traveling salesman, wakes up to find himself transformed into a "ungeheures Ungeziefer", literally "monstrous vermin", often interpreted as a giant bug or insect. He believes it is a dream, and reflects on how dreary life as a traveling salesman is. As he looks at the wall clock, he realizes he has overslept, and missed his train for work. He ponders on the consequences of this delay.

Gregor becomes annoyed at how his boss never accepts excuses or explanations from any of his employees no matter how hard working they are, displaying an apparent lack of trusting abilities. Gregor's mother knocks on the door and he answers her. She is concerned for Gregor because he is late for work, which is unorthodox for Gregor. Gregor answers his mother and realizes that his voice has changed, but his answer is short so his mother does not notice the voice change. His sister, Grete, to whom he was very close, then whispers through the door and begs him to open the door. All his family members think that he is ill and ask him to open the door. He tries to get out of bed, but he is incapable of moving his body. While trying to move, he finds that his office manager, the chief clerk, has shown up to check on him. He finally rocks his body to the floor and calls out that he will open the door shortly.

Feeling offended by Gregor's delayed response in opening the door, the clerk warns him of the consequences of missing work. He adds that his recent performance has been unsatisfactory. Gregor disagrees and tells him that he will open the door shortly. Nobody on the other side of the door could understand a single word he uttered (Gregor was unaware of the fact that his voice has also transformed) and conclude that he is seriously ill. Finally, Gregor manages to unlock and open the door with his mouth. He apologizes to the office manager for the delay. Horrified by Gregor's appearance, his mother faints, and the manager bolts out of the apartment. Gregor tries to catch up with him, but his father drives him back into the bedroom with a cane and a rolled newspaper. Gregor injures himself squeezing back through the doorway, and his father slams the door shut. Gregor, exhausted, falls asleep.