On the morning of his thirtieth birthday, Josef K., the chief clerk of a bank, is unexpectedly arrested by two agents from an unidentified agency for an unspecified crime. The agents discuss the situation with Josef in the unoccupied room of his fellow lodger Fräulein Bürstner, in the unexplained presence of three junior clerks from Josef's bank. Josef is not imprisoned, but left free to go about his business. His landlady, Frau Grubach, tries to console Josef about the trial. He visits Bürstner to explain the events, and then kisses her.
Josef is invited to appear at the court's address the coming Sunday, without being told the time or location. After a period of exploration he finds the court in the attic of a dilapidated working-class tenement block, at the back of a young washerwoman's home. Josef is rebuked for his lateness and mistaken for a house painter rather than a bank clerk. He arouses the assembly's hostility after a passionate plea about the absurdity of the trial and the falseness of the accusation, despite still not knowing the charges. The proceedings are interrupted by a man sexually assaulting the washerwoman in a corner. Josef notices that all the assembly members are wearing pins on their lapels which he interprets as signifying their membership of a secret organisation.
The following Sunday Josef goes to the courtroom again, but the court is not in session. The washerwoman gives him information about the process and attempts to seduce him before a law student, the man who assaulted her the previous week, takes her away, claiming her to be his mistress. The woman's husband, a court usher, then takes Josef on a tour of the court offices, which ends after Josef becomes extremely weak in the presence of other court officials and defendants.
Josef finds that Fräulein Montag, a lodger from another room, has moved in with Fräulein Bürstner. He suspects that this is a coy manoeuvre meant to distance him from Bürstner, and resolves that she will eventually fall for his charms.
One evening, in a storage room at his own bank, Josef discovers the two agents who arrested him being whipped for soliciting bribes from Josef, which he had complained about at court. Josef tries to argue with the flogger, saying that the men need not be whipped, but the flogger cannot be swayed. The next day he returns to the storage room and is shocked to find everything as he had found it the day before, including the whipper and the two agents.
Josef is visited by his uncle Karl, who lives in the country. Worried by the rumors about his nephew, Karl introduces Josef to Herr Huld, a sickly and bedridden lawyer tended to by Leni, a young woman who shows an immediate attraction to Josef. During a conversation between Karl and Huld about Josef's case, Leni calls Josef away for a sexual encounter. Afterwards, Josef meets his angry uncle outside, who claims that Josef's lack of respect for the advocate, by leaving the meeting and romantically engaging with the woman who is apparently Huld's mistress, has hurt his case.
Josef has become increasingly preoccupied by his case, to the detriment of his work. He has further meetings with Huld, and continues to engage in discreet trysts with Leni, but the advocate's work appears to be having no effect on the proceedings. At the bank, one of Josef's clients recommends he seek the advice of Titorelli, the court's official painter. Titorelli outlines the options he can help Josef pursue: indefinite postponement of the process, or a temporary acquittal that could at any point result in re-arrest. Unequivocal acquittal is not a viable option.
Suspicious of the advocate's motives and the apparent lack of progress, Josef finally decides to dismiss Huld and take control of matters himself. Upon arriving at Huld's office, he meets a downtrodden merchant, Rudi Block, who offers Josef some insight from a fellow defendant's perspective. Block's case has continued for five years and he has gone from being a successful businessman to being almost bankrupt and is virtually enslaved by his dependence on the lawyer and Leni, with whom he appears to be sexually involved. The lawyer mocks Block in front of Josef for his dog-like subservience. This experience further poisons Josef's opinion of his lawyer.
Josef is put in charge of accompanying an important Italian client to the city's cathedral. While inside the cathedral, a priest calls Josef by name and tells him a fable (which was published earlier as "Before the Law") that is meant to explain his situation. The priest tells Josef that the parable is an ancient text of the court, and many generations of court officials have interpreted it differently.
On the eve of Josef's thirty-first birthday, two men arrive at his apartment. The three walk through the city, and Josef catches a brief glimpse of Fräulein Bürstner. They arrive at a small quarry outside the city, and the men kill Josef, stabbing him in the heart with a butcher's knife while strangling him. Josef summarizes his situation with his last words: "Like a dog!"
