Logan Thibault (Zac Efron), a U.S. Marine serving in Iraq, witnesses a Marine called "Aces" die attempting to aid one of his men during an ambush. The following morning, he finds a picture of a young woman on the ground just before a mortar attack destroys where he had been sitting, killing many around him. Unsuccessful at finding the photo's owner, Logan keeps it. Logan's squadmate declares the woman in the picture Logan's "guardian angel" just before an explosion destroys their Humvee.
Logan returns to Colorado to live with his sister's family, who have been looking after his dog, Zeus. Suffering from PTSD and survivor guilt, he decides it is best to leave, and departs to search for the woman in the photo. Logan and Zeus walk to Louisiana, where a lighthouse in the picture has provided a clue. He shows the photo around town and a local resident warns him that the woman used to be married to a friend of his, a local deputy sheriff.
Logan finds the woman, Beth Green (Taylor Schilling), but has difficulty explaining why he is there. She assumes he wants to apply for a job, and her grandmother, Ellie (Blythe Danner) hires him. At first, Beth is irritated by Logan's presence, but she begins to warm to him as Logan's calm presence, willingness to work, and competence in repairing machinery are demonstrated. Logan develops a supportive relationship with Beth's son, Ben, who is without positive male influence since the death of Beth's brother, Drake.
Beth's former husband, Sheriff Deputy Keith Clayton—the son of the town's judge—is immediately suspicious of Logan. He is brusque and overbearing with the former Marine. He discourages Ben from playing the violin around him, leading to Ben to practising in his tree house. When Ben returns bloodied from a charity baseball game, Beth and Keith have an argument, and Keith threatens to use his connections to take full custody of Ben. Beth is anxious over Keith's short temper, and is fearful of losing her son to him.
On the anniversary of Drake's death, Beth becomes distraught and Logan comforts her. Keith tries to stop the budding relationship between Beth and Logan, but Beth stands up to Keith, showing that she is not intimidated by him anymore. Keith learns that Logan was asking about her when he first arrived in town and steals the photo, telling Beth that Logan has been stalking her. Her trust destroyed, Beth is distraught and sends Logan away. Ellie tries to soften Beth, explaining to her that it isn't Logan's fault he survived and Drake did not.
An intoxicated Keith sees Logan walking with his dog and angrily confronts him, drawing his gun while people on the street begin to panic and run. Logan disarms Keith, turning the weapon over to another officer. He then heads home to pack and finds a photo of Beth's brother, Drake, inside a book that Ben had given him. The tattoo on Drake's forearm says "Aces". He returns to Beth's house to tell her what he knows of how Drake died.
At Judge Clayton's, Keith is shocked and embarrassed over what he did though his father tells Keith it will all blow over before the election. Keith walks out into a gathering storm, leaving his badge behind and goes to Beth to plead for a reconciliation. When Beth gently but firmly refuses, Keith threatens to take Ben away. Ben overhears this and runs out into the storm, followed by Keith and Beth, just as Logan arrives. Ellie urges Logan to follow. Ben is en route to the tree house, but the rope bridge gives way and he falls into the river along with his father, just as Beth and Logan arrive. Keith, caught in the rope of the bridge, calls to Logan who grabs Ben and hands him to Beth. Before Logan can return for Keith, the tree house falls and Keith disappears.
Back home, Beth thanks Logan for saving her son. Logan explains that Drake died saving one of his own men. He starts to leave, but Beth runs after him says that he belongs with them. Later, Logan, Beth, Zeus and Ben, celebrate Ben's 9th birthday together.