The novel starts for the readers from as sudden event as it is for its main character, Joseph K. who has just turned thirty. But instead of a party the surprise for his birthday is quite nasty: instead of the servant with the breakfast there are several men in black suits in his room and they inform him that he is arrested. One of the two guards who broke into his lodging house and captured him, tells him that Joseph is under arrest but refuses to name the reason, saying that he is just doing his job and doesn’t know neither the charges nor the terms of arrest. The guards behave politely and Joseph feels no fear, just something between irritation and amusement. He knows that he is not guilty, so everything looks just like a practical joke. Still, the people in the room are deadly serious about their job, so, gradually, Joseph starts to worry. The warrant for the arrest wasn’t shown to him and the two people don’t look like policemen. Joseph tries to guess what is really happening, but the guards, responding perfectly politely to is irritated questions, say he’ll get all the answers on the trial.
The guards ask him to go to the next room that belongs to another tenant, Fraulein Burstner. She isn’t in her room at the time, so the intruders use the room to briefly interrogate poor Joseph. After some seemingly unimportant questions, the inspector says that it is enough for preliminary investigation of his case, so for now Joseph can return to his ordinary life until the trial. Joseph is escorted to the bank where he works by his colleagues - they were present in his room all the time, but Joseph didn’t recognize them, because all the uninvited guests looked equally dull and colorless in their identical black suits and neutral face expressions. Three of his colleagues sit with him in a taxi, in eerie but polite silence.
Joseph never thought that such a ridiculous incident could happen to him. He considers himself a respectable and successful man with a solid position in the society. He is a proctor in a big bank, with his own spacious office, lots of people and a good house with a personal servant. He is admired by the colleagues, has a mistress who admires him too and until that morning Joseph considered his life steady and peaceful. After the working day he returns home and discusses the strange incident with his mistress, Frau Grubakh. To his surprise she already knows about everything and keeps calm, saying that it’s nothing and Joseph also shouldn’t worry too much about it and not to take it to heart. In the end she adds that it could be something “scientific” connected to his arrest.
Then Joseph apologizes to his landlady for all the mess caused by his “arrest”, but she also doesn’t seem to mind, saying that it was nothing. The last person Joseph needs to apologize to is Fraulein Burstner, whose room was used for interrogation and turned upside down. Fraulein Burstner is startled by Joseph’s story, but gradually gets interested and when Joseph offers her to dramatize it, she allows. Joseph plays too loud and the little nephew of the landlady, who was sleeping in another room, wakes up. Fraulein Burstner notices this and asks Joseph to leave, which he does, giving her a hug before it.
The next day goes as usual. Joseph tries to get immersed into work completely to forget the ridiculous case. But soon his phone rings and polite and detached voice informs him that the preliminary investigation of his case is appointed on Sunday. The anonymous executive adds, in the same perfectly polite manner, that they all are interesting in closing the case as soon as possible, but there are some complications and the case itself is very difficult, so they have to proceed with caution. When the conversation ends, Joseph still stands, holding the phone, and is found by his old rival, the deputy director, that way.
Despite still thinking that all the case is a huge mistake, Joseph prepares himself. He rises early on Sunday, puts his best suit on and goes to the address mentioned by the executive. To his surprise, the court seems to be situated in the impoverished working-class district, in the apartment building. He wanders around, knowing that he is very late to the beginning of the trial, but suddenly, in one of the worst buildings he finds a woman washing the clothes. He asks her about the court and she appears to know where to go. The woman escorts him to the hall, looking not much better than the rest of the building, full of different people with the same dull and neutral face expressions he saw at the day of his arrest. On the one side of the hall there is a stage, where another man stands. He pretends to be the judge and he berates Joseph for being late for an hour and five minutes. After that Joseph is allowed to speak and he says his carefully prepared speech, accusing the court of corruption, blaming them of violating the rules of arresting and laws, exposes the methods of investigation and invalid documentation presented in the plain notebooks. His speech is perfectly credible and logic, but the reaction of the audience is strange. They laugh, applause and murmur, looking shocked and amused, as if instead of a prepared and well-said speech they listened to the babbling of a lunatic. Finishing his talk, angry Joseph puts back his hat on his head and turns away to leave. The investigator warns him that he has just made a great damage to his case and will make even more if he leaves without interrogation. Joseph laughs into his face and leaves.
Despite no calls from the court followed his leave, Joseph just can’t calm himself. On the next Sunday he returns to the building to talk to the court officials privately. He meets the same woman again and she tells him that the court isn’t on the session today. She talks to him a bit and suddenly Joseph feels that he is sexually attracted to her and almost can’t resist the temptation. The woman (who appeared to be the wife of the court usher) expresses sympathy for him, saying that she knows how serious and complicated his case is. Still flirting with him, the woman allows him to go to the courtroom and have a look. When Joseph enters the room he is shocked to discover that the “evidences” and “documents” - the notebooks he criticized on the last session - are porn novels. Suddenly a young law student enters the courtroom and the usher’s wife gladly goes with him, now showing him signs of affection. Soon, her husband enters the room and he seems perfectly fine with such her behaviour. Instead of being angered, he turns to Joseph, giving him some advice, but calling him accused. The usher offers him to take a tour and they both go through the building, climbing the surrealistic stairs and passing long dark corridors that seem to be abandoned long ago. When they finally reach the seemingly normal offices, there are clerks busy with their papers and some other people who are waiting for something. They look weary and exhausted and they are also called accused. Suddenly, Joseph feels sick, he can’t breath in the muggy office and the usher immediately orders to escort him out. In a few minutes Joseph feels better and decides to return home.
Though his life is seemingly normal, for Joseph it starts to resemble a surrealistic dream. He notices some minor but strange events and changes connected with the trial. The trial itself seems to have some sick logic that just can’t be grasped by the sane mind. Moreover, despite Joseph keeps the trial secret from everyone except the three women he talked on the first day, everyone seems to know about it. Colleagues, neighbors and even bystanders sometimes say something about the trial. Some of them later participate in the process of it and this only fuels Joseph newly acquired paranoia.
Once, while Joseph goes to the closet in the bank, he suddenly sees that the guards who arrested him in the very first morning, are there, spanked with rods by an executioner. When shocked Joseph asks them all what is happening here, the executioner explains that the guards are punished because of Joseph’s complaint to the investigator. Astonished Joseph just stands there and watches the execution. Still, both victims and executioner are again very polite to him. Joseph feels that he is losing his mind. Everyone involved looks perfectly logical and sane presenting their point: the minor officials who are just doing their job, complaining about it and compassionately giving Joseph advice, the executives who are dull and tired, just being indifferent and polite… but nothing can be gathered into the bigger picture. Joseph tries to meet with higher authorities to hear what this all case is about, but they remain inaccessible to him. The overwhelming bureaucracy just doesn’t allow him to fight the system.
The trial continues, the procedures become more complicated and tiresome. One day Joseph receives a notice from his uncle, who came from the countryside to help him with the case. He lectures Joseph for being so reckless while dealing with such a serious matter as trial. Not listening to the refusals, he takes Joseph to his friend, a defensive lawyer named Huld. Unfortunately, Huld is sick at the moment, so he accepts his guests being bedridden. He seems very competent and comes up with a valid plan of defence. There is another person in the room: the young and pretty nurse named Lenny who takes care of Huld while he is sick. Joseph, sick of lawyer’s long and boring speech, takes a break and leaves the room. Lenny follows him, clearly showing that she wants to have sex with him. She takes him to the lawyer’s study and they make love on the carpet there. When Joseph returns, his uncle waits for him outside the house and he is enraged. He says that Joseph just destroyed his chance to get the best defensive lawyer, because it was too obvious why he left the room with Lenny. However, Huld still agrees to represent Joseph in the court and they start working on his defence. Joseph also has casual sex with Lenny every time he comes to Huld, but this never grows into the actual relationship.
Joseph learns about the court painter, Mr. Titorelli and asks him for a meeting - thinking that Titorelli may have some connections in the court. He meets Titorelli in his studio. Titorelli shows Joseph the portraits of judges and says that from his scarce experience it seems that the only hope for Joseph is to endlessly defer his final judgement. Grateful, Joseph buys some of his paintings and exits - but suddenly the door opens not to the street but to the courtroom.
The trial takes all Joseph’s resources: he can’t sleep properly and therefore he can’t work as good as he used to. The exhaustion causes a flu, so Joseph stays at home for some time, working with business papers. He is afraid that his reputation in the bank is damaged. Suddenly one of his important bank clients asks him to show the local cathedral to one of his Italian friends. Despite his illness, Joseph comes to the cathedral where the meeting is appointed. It starts raining outside, so Joseph decides to enter the cathedral to wait for Italian there. Suddenly, someone strictly calls him. Joseph turns around to see a priest who calls himself a prison chaplain. He says that Joseph’s situation is very bad and, after some hesitation, Joseph agrees: he doesn’t see any progress in his trial. He and the priest discuss the parable about the man who searches the way to the Law but the gatekeeper stands on his way. Joseph tries to understand the parable, but finds the interpretation rather contradictory. He blatantly asks the chaplain to help in his case, but he refuses.
Seeing that Huld can’t do anything to help him, Joseph decides to dismiss him and become his own defence. He comes to Huld to say that, but the lawyer is now talking to another client, Mr. Block, a merchant, who is in the similar situation and has already sold everything he had to pay for defense. Joseph says that he doesn’t need Huld’s service anymore. Huld asks if Joseph is sure and continues to berate block in front of Joseph. Joseph doesn’t want to see it and leaves.
A year passes and the trial still continues. Joseph wakes up in the morning of his thirty-first birthday and again the two men in black suits are there. This time Joseph doesn’t have the will to resist, just dressing up and waiting for the following borders. They take him out of the house and go with him to the abandoned quarry. Staying polite, they take away his jacket and shirt, making him kneel and put his hand on a rock. One of them takes the knife. Joseph thinks that they are going to kill him and wants to grab the knife and stab himself not to let them do so, but he feels unable to move. He desperately thinks about the judge who he has never seen and some missed arguments that could prove he is not guilty, while one of the executioners grabs his throat and the other stabs him twice in his heart.