The film is set in the Mid-Coast town of Camden, Maine. Ruth Fowler (Sissy Spacek) and Matt Fowler (Tom Wilkinson) enjoy a happy marriage and a good relationship with their son Frank (Nick Stahl), a recent college graduate who has come home for the summer. Matt is a well-respected doctor in the community.Frank has fallen in love with an older woman with children (Jason and Duncan), Natalie Strout (Marisa Tomei). Frank is also applying to graduate school for architecture but is considering staying in town for another year, and work in the fishing industry, to be near to Natalie. Natalie's ex-husband, Richard Strout (William Mapother), whose family owns a local fish-processing and delivery business, is violent and abusive. Richard tries to find a way into his ex-wife and son's lives, going to increasingly violent lengths to get his intentions across to Natalie. Richard is specifically angry that Natalie picked a college boy Frank, over him. Natalie tries hard to communicate that Richard is not the right father figure for her kids.Ruth is openly concerned about Frank's relationship with Natalie, while Matt sees past his wife's worries. Natalie is not divorced yet. Frank assures Ruth that his relationship with Natalie is a summer fling. But one day, Richard finds Frank and Natalie in a park and proceeds to assault Frank. Ruth wants to press charges, but Frank refuses as he doesn't want Natalie and the kids to be dragged into police business.Frank rushes to Natalie's home one evening after receiving a frightened phone call from one of her children. He arrives to find the living room trashed and Natalie in distress. She tells him Richard just left, but he returns almost immediately. Natalie takes the boys upstairs, and Frank insists through the locked front door that Richard leave. He feigns doing so, only to break in through the back door with a handgun. In the ensuing skirmish, Richard shoots and kills Frank. Natalie came downstairs moments later and found Richard standing over Frank's body with a gun and blood on his hands.Though equally devastated, Matt and Ruth grieve in different ways, with Matt putting on a brave face while Ruth becomes reclusive and quiet.The tension between the pair increases when they learn that the lack of a witness (as Natalie also testifies that she only heard a shot, and that she did not actually see Richard shoot Frank) to their son's shooting allows the killer to avoid murder charges, since the district attorney may have difficulty proving that Richard killed Frank intentionally, as opposed to accidental manslaughter during a struggle, which defense attorney Marla Keyes (Karen Allen) argues. Under accidental manslaughter charges, Richard will likely spend only 5-15 years in prison. And the trail will be after 12-18 months.Richard is set free on bail, paid by his well-to-do family, and both Matt and Ruth are forced to see Richard around town. Ruth and Matt go about their lives as normally as they can. Matt tries to lose himself in his practice, household repair jobs, and poker nights with his friends. Frank was very fond of lobster fishing and Matt takes the boat out and relive the memories of his son. Matt is not comfortable with the manslaughter charge and speaks to their lawyer, who says that they are doing the best they can. To find new evidence, Matt reaches out all of Richard's friends to see if he said anything to them. Natalie approaches Ruth at work and attempts to apologize, but Ruth slaps her before dismissively returning to her papers. Natalie leaves in tears. Later that day, Ruth accidentally runs into Richard again.The couple retreat with friends Willis (William Wise) and Katie Grinnel (Celia Weston) to a secluded cottage for a weekend. The silence between the couple erupts in an argument where each is confronted with the truth about each parent's relationship with their son: Ruth was overbearing, and Matt let him get away with everything. With the strain between them broken, the couple is finally able to find common ground in their grief.Matt abducts Richard at gunpoint, saying he's arranged for Richard to jump bail and leave the state, so as to spare them the pain of seeing him in Camden. He forces Richard to "pack clothes for warm weather" and plants a train schedule in his apartment. He then makes Richard drive them to the Grinnel cabin, where Willis is waiting with another vehicle. He begins to load Richard's belongings, but Matt hesitates - and then shoots Richard, killing him. Willis admonishes Matt for not following the plan. Matt responds that he couldn't wait. The two bury Richard's body deep in the woods but are stuck unexpectedly at a bridge crossing on their return home. Willis laments that this cost them nearly an hour - meaning they arrive back in town just after sunrise instead of in darkness.Matt returns home to find Ruth awake. She asks, "Did you do it?" Matt appears troubled and unresponsive. He climbs into bed and turns away from her. She asks if he's okay, and Matt haltingly describes a photo he saw in Richard's apartment of him with Natalie in a loving pose but cannot explain why it affected him. Finally, Ruth gets up to make coffee. She calls from the kitchen, "Matt, do you want coffee?" but he doesn't answer.