After two years of training, Jim ships out to sea, where he performs his duties well and quickly rises to a position of chief mate on a ship while still quite young. Injured in a storm while aboard ship, Jim undergoes a long period of recovery below deck and is eventually left behind at an eastern port to recuperate further at a hospital while the ship moves on with its voyage. First searching for a ship that can take him back home once recovered enough to travel, Jim eventually gives up that idea and instead takes a berth as chief mate on a steamer ship called the Patna.

As the Patna moves forward on its voyage, Jim spends much of his time on watch dreaming about his future great achievements. Jim is described as separate from the other seamen, with a sense of his superiority to the other crew. One night, the Patna unexpectedly strikes an object in the ocean while the chief engineer is drunk. The chief engineer, Jim, and the German captain all pitch forward with the impact, and no one is sure what has happened. An ominous noise like rolling thunder then emanates from the ship below deck.

Jim is called to give testimony in an inquiry as to what happened on the ship after hitting the object. Jim testifies that he was told to tell no one about the incident for fear of creating a panic on the ship. Jim investigated and believed that a large hole had been created in the ship below the water line. The ship’s bulwarks bulged ominously. Jim describes how the second engineer, who had broken his arm in the incident, expressed his belief that the ship would go down. As Jim is getting more and more frustrated with how his testimony is being received, his eyes focus on Captain Marlow, a British seaman who is among those listening to the testimony.

Marlow, an experienced ship captain, picks up the narrative in first person and describes attending the inquiry. The affair involving the Patna has become notorious, and thus the inquiry draws a large crowd. When the Patna’s captain arrives, the British master attendant proceeds to dress him down in words loud enough for many to hear. Three other crew members wait for the captain to return from that meeting, and Marlow sees Jim for the first time, noting that he appears unperturbed. Meanwhile the German captain of the Patna curses Captain Elliot and the English generally for the way they are handling the inquiry and insulting him personally. The Patna’s captain is driven away from the proceedings in a horse-drawn vehicle, never to be seen by Marlow again. A local surgeon testifies that the Patna’s chief engineer is now suffering from delirium tremens after a spectacular drinking bout following the incidents on the Patna.

Marlow’s description of the inquiry continues, though it is clear the authorities do not expect to be able to find out what object the Patna actually struck. The presiding magistrate, Captain Brierly, is described as appearing self-satisfied during the proceedings themselves, though Marlow also indicates he dies by suicide barely a week after the inquiry concludes. Brierly is frustrated that Jim has become the focus of the inquiry simply because he is willing to appear and answer questions while the captain of the Patna has already taken off. Brierly even suggests the inquiry would end at once if Jim simply went away, and no one would blame him. At one point, while everyone is leaving the proceedings during a recess, Jim apparently believes that Marlow has referred to him as a cur, though Marlow’s narrative indicates the remark was made by another spectator in reference to an actual dog. Jim eventually perceives his mistake, but he still questions why Marlow would have stared at him throughout the proceedings.

Marlow invites Jim to share a meal with him. During the meal, he notices that some wine seems to help Jim relax. Jim explains that he feels compelled to stay and give his testimony even though the Patna’s captain has left to avoid testifying. Jim talks about his family and indicates he will never be able to face his father again after the incidents on the Patna and the inquiry. He describes how he and three others of the crew were picked up from a long boat, though in fact the Patna had not sunk, and its passengers survived after being hauled by another boat to safety. Still, Jim attests that the night of the incident he was certain the ship would go down at any moment based upon the damage he saw in the ship’s bulwarks.

Jim narrates his escape from the Patna with the other crewmen. Following the collision, Jim asks the ship captain if he is going to do something, to which the captain replies that he is going to clear out from the ship. Other crew members are struggling to release a long boat from the ship, and they call on Jim to help, though at that point he plans to go down with the ship if it comes to that.

While they are still struggling to release the boat, a storm comes in upon the ship. With this added problem, the crew is certain that the ship will go down. Jim watches while the other crew members frantically struggle almost comically to release the boat. One of the other crew members, a man named George, collapses from an apparent heart attack. Three other crew members are calling for the collapsed crew member to jump into the longboat with them, not knowing George has collapsed. Instead, it is Jim who at the last moment impulsively jumps in, though he does not seem to have a clear memory of that action when he later describes it.

In the black darkness and rain, those in the longboat are barely even able to see each other. From the longboat, Jim sees the yellow gleam of a mast-head light on the Patna, and he tells Marlow that he was terrified to see the Patna still afloat. When the crew members in the longboat look back at the Patna again, they can no longer see a light, so they believe the ship has indeed gone down. Everyone on the longboat is silent for a time, believing that the 800 others aboard the Patna are drowning. The other crew members in the boat still believe it is the collapsed crew member George who has entered the boat with them until they finally recognize Jim. They berate Jim and even threaten to throw him overboard, but nothing happens.