An English fishing village. During a coroner’s inquest at the town hall, the lawyer Swallow questions the fisherman Peter Grimes about the death of his apprentice during a storm at sea. Though the room is crowded with villagers hostile to Grimes, Swallow accepts the man’s explanation of the event and rules that the boy died accidentally. He warns Grimes not to take on another apprentice unless he lives with a woman who can care for the boy. When the hall empties, Ellen Orford, the schoolmistress, asks Grimes to have courage and promises to help him find a better life.
On a street by the sea, the women repair nets as a group of fishermen head for the Boar, a tavern kept by Auntie. Other villagers arrive: the Methodist fisherman Bob Boles, the widow Mrs. Sedley, and Balstrode, a retired sea-captain who warns that a storm is approaching. Grimes calls for help from the harbor to land his boat, but only Balstrode and the apothecary Ned Keene lend him a hand. Keene tells Grimes that he has found him a new apprentice at a workhouse. When the carrier Hobson refuses to fetch the boy, Ellen offers to go with him. The villagers make hostile comments, and she accuses them of hypocrisy (“Let her among you without fault cast the first stone”). As the storm rises and the crowd disperses, Grimes is left alone with Balstrode, who tries to convince him to leave the village. The fisherman explains that first he has to make enough money to open a store and marry Ellen.
That night, as the storm rages, the villagers gather at Auntie’s tavern. Auntie’s “nieces” are frightened by the wind and Bob Boles gets into a fight with Balstrode over one of them. When Grimes enters, there is a sudden silence, and he begins talking to himself, mystifying everyone (“Now the Great Bear and Pleiades”). The drunken Boles tries to attack Grimes. In an attempt to restore quiet, Ned Keene starts singing a sea shanty (“Old Joe has gone fishing”). When Hobson and Ellen arrive with the new apprentice, John, Grimes immediately takes the boy back into the storm and to his hut.
On Sunday morning, as Ellen and John are watching the villagers go to church (“Glitter of waves”) she discovers a bruise on the young boy’s neck. Grimes comes to take John fishing. Ignoring Ellen’s concerns, he hits her and drags the child off. Auntie, Ned Keene, and Bob Boles have observed the incident and tell the congregation about it as they come out of church. The men decide to confront the fisherman, and despite Ellen’s protests, Boles leads the angry mob off to Grimes’s hut. Ellen, Auntie, and the nieces remain behind, reflecting on the childishness of men.
At his hut, Grimes orders John to dress for work. He dreams of the life he had planned with Ellen, but his thoughts return to his dead apprentice. As he hears the mob approaching, he rushes John out the back door. The boy slips and falls down the cliff; Grimes escapes. Bob Boles and the Rector find the hut empty and orderly and decide that they have misjudged Grimes. The villagers disperse, except for Balstrode, who looks over the cliff and knows better.
A dance is under way in the town hall. Outside, Mrs. Sedley tries to convince Ned Keene that Grimes has murdered his apprentice. Balstrode enters with Ellen and tells her that Grimes’s boat has returned but that there is no sign of him or the boy. He has also found John’s wet jersey, and Ellen remembers embroidering the anchor on it (“Embroidery in childhood was a luxury”). Mrs. Sedley has overheard the conversation and informs Swallow that Grimes’s boat is back. Once again, the crowd sets off on a manhunt.
Grimes, deranged and raving, listens to the villagers shouting his name in the distance. He hardly notices Ellen and Balstrode, who try to comfort him. Ellen asks Grimes to come home, but Balstrode tells him to sail out and take his own life. He helps Grimes launch the boat, and then leads Ellen away. As dawn breaks, the villagers return to their daily chores. Swallow tells them that the coast guard has reported a sinking boat, but no one listens to him.