In the coastal village of Camden, Maine, Frank Fowler spends his last summer before college with his girl friend, the older and soon-to-be divorced Natalie Strout. Frank works part-time on a lobster boat and is frequently accompanied by his father Matt, the town doctor. When Frank takes Natalie’s son Jason out on the boat one day, Matt comes along and teaches Jason about the art of trapping lobsters. A few days later, Matt and his wife, high school choir director Ruth, throw a picnic to help Frank celebrate the birthday of Natalie’s other son Duncan. At the party, Natalie attempts to befriend Ruth, but is interrupted by the arrival of her estranged, abusive husband Richard, the son of the wealthy owner of the large, local fish-processing plant. Uneasy about Richard seeing the familiarity with which his sons treat Frank, Ruth asks Matt if they should intervene, but Matt feels there is no need to interfere. Later that week, Matt goes to the boat looking for Frank, only to recall that his son has a college interview. Arriving at home, Matt is amused and mildly displeased to learn that Frank skipped the interview to meet Natalie. That afternoon at Jason and Duncan’s T-Ball game, when Ruth asks Frank about his interview, he lies, declaring that it went well. When Ruth obliquely expresses her concern about Frank dating Natalie, Frank brusquely assures her their relationship is only a passing summer affair. Later, Natalie arrives home to find that Richard has broken in, claiming to want to give the boys his own T-Ball trophy. When Richard declares his intention to move back in and repair their relationship, Natalie criticizes him for not being involved in their sons’s lives and orders him to leave. An aspiring architect major, Frank begins to vacillate about going to college in the autumn, but when he suggests to Natalie that he might take off a year, she advises circumspection. That same night when Ruth returns home after a choir rehearsal for the Labor Day festival, she is distressed to find Matt treating Frank for a black eye and several cuts. Frank explains that Richard confronted him at Natalie’s, resulting in a brief scuffle. Alarmed, Ruth wants to report the fight to the police, but Frank insists an investigation will only frighten Jason and Duncan. Ruth then angers Frank by demanding that he stop seeing Natalie. In private, however, Matt refuses to agree with Ruth's condemnation of Frank and Natalie's relationship. Several days later, Matt visits Frank at the pier to inquire why he has spent so little time at home. Suspicious that Ruth has sent Matt, Frank chafes at his parents’ expectations and implies that he may continue working on the lobster boat and skip college. That night, however, Frank joins Matt for their usual poker game with a handful of neighbors, including Matt’s best friend, diner owner Willis Grinnel. The players grumble when Matt hesitates over his hand, prompting one of the men, Carl, to recite dour poetry until the game continues. Late that night, Frank rebuffs Ruth’s attempt to discuss Natalie. The next day, Frank is pleased to receive a phone notification of his college acceptance, but the call is interrupted by Jason, who pleads for Frank to come to Natalie’s at once. Frank finds Natalie’s home in shambles because of an angry outburst by Richard, but Natalie fears contacting the police will traumatize the boys. When Frank and Natalie see Richard returning to the house, Frank orders her upstairs then tells Richard he will summon the police, but Richard breaks in through the back door anyway. Upstairs, Natalie and the boys hear the men quarreling, but before Natalie can run downstairs, a gun is fired. Natalie finds Frank lying dead, shot in the face. Matt and Ruth are devastated by Frank’s death and attend his funeral in a daze. Over the next few weeks, the Fowlers fall into private anguish, retreating from each other and their friends. After returning to work, Matt meets Willis at the diner and admits that he and Ruth are unsure about attending Richard’s bail hearing. At the bail and probable cause hearing, Natalie’s testimony contradicts her police statement, revealing that she did not witness the gun’s discharge. Afterward, the district attorney explains to Matt and Ruth that Richard’s wealthy family paid his bail and that his trial will probably not occur for twelve to eighteen months. Ruth is outraged when the lawyer admits that as there was no eyewitness to the killing, Richard will probably be charged only with manslaughter, which would result in a jail sentence of as few as five years. The following day, when Matt visits Natalie at the convenience store in which she works, she struggles to apologize for her damaging testimony. That weekend, Matt and Ruth accompany the Grinnels to their remote cabin upstate. Upon returning to Camden, Ruth resumes preparing the girls’ choir for their Labor Day performance. While visiting Frank’s grave Ruth meets a solicitious Father McCasslin, but she finds his offer of solace empty. Matt returns to his weekly poker game to find his friends strained and uneasy around him, until Carl’s moving recital of an ode to youth breaks the tension. In town, Ruth is disturbed to see Richard walk by arm in arm with a woman, while Matt sails alone sadly. Later, Matt confronts the D.A., insisting that manslaughter is an unacceptable charge, but there is little the lawyer can do to mitigate the circumstances. Later, Matt follows Tim, a friend of Richard’s, to a bar at the edge of town, desperately pleading without success for some information about Richard's actions on the day of the murder. When Natalie goes to see Ruth at the high school to express regret and offer her support, an embittered Ruth slaps her. Stopping for groceries on the way home, Ruth is disturbed to see Richard again. At home, Matt questions Ruth over her apparent anger, but when she scoffs at Matt for belatedly wanting to discuss their grief, a vicious argument ensues. Ruth accuses her husband of being too lenient with Frank and encouraging his affair with Natalie out his own frustrations, while Matt declares that Ruth’s overbearing, controlling nature drove Frank to Natalie. After their outburst, Matt and Ruth are contrite over the harsh words exchanged, then Ruth reveals that she is unnerved by constantly seeing Richard free in town. A few days later, Matt meets Willis and the men discuss the distress and anxiety brought about by the overwhelming sense that Richard will never pay for his crime. Willis wonders if Matt and Ruth have considered leaving Camden, but Matt declares that it would not ease their suffering. On Labor Day, the townspeople gather to hear the girls’ choir, while Matt slips away. Late that night, Matt intercepts Richard closing down the bar, where he now works, and at gunpoint forces him to drive to his apartment. There, the confused Richard tries to explain why he killed Frank, but Matt refuses to listen. Matt orders Richard to jump bail and leave town because he and Ruth cannot bear his presence in Camden. Uneasy about Matt's offer to pay for his flight out of state, Richard nonetheless follows his directive to drive out of town, and is relieved when they arrive at Willis’ remote cabin. Once there however, Matt impulsively shoots and kills Richard, telling the startled Willis that he could not wait to kill Richard together, as they had discussed previously. Matt and Willis wrap up Richard’s body and bury it deep within the forest, then return to Camden just before sunrise. Matt disposes of his dirty clothes, then wearily climbs into bed, where an anxious Ruth asks him, "Did you do it?"