Lynsey, Jennifer Lawrence, a soldier in the United States Army Corps of Engineers during the Afghanistan War, is recovering from a traumatic brain injury. She undergoes physical therapy with a kindly professional caretaker, Jayne Houdyshell, and gradually regains her motor skills. Unable to afford further treatment, she is forced to return home to New Orleans.
Staying in her childhood home with her unreliable mother Gloria, Linda Emond Lynsey finds a job cleaning pools. When the truck once belonging to her brother breaks down, she finds help from Brian Tyree Henry, an auto mechanic. Struggling to adjust to daily life and her new medications, she explains to her doctor that she was injured by an IED in Afghanistan, but is determined to return to duty.
Lynsey and James become unlikely friends, and after he helps her avoid unwanted advances at a bar, she reveals that she is a lesbian. He confides in her about losing his leg in a car crash on the Lake Pontchartrain Causeway, and she opens up about her unhappy memories of home, including her brother Justin's problems with drugs. James drunkenly invites her to move in with him, in the house he used to share with his sister and her son.
Despite her mother's objections, Lynsey commits herself to redeployment, and finds herself swimming in an out-of-town client's pool. She continues to spend time with James, bonding over sno-balls and their shared physical and mental trauma. Her doctor fears the impact of her injury on her mental health, warning of the strong link between trauma and her depression. Their conversations reveal how each has learned to carry pain while seeking moments of light in daily life.
When Lynsey convinces James to join her in the pool, he reveals that he was driving when the car crashed; his nephew was killed, leaving him estranged from his sister. Comforting James, Lynsey impulsively kisses him. Embarrassed, she declares that she was acting out of pity, leading to an argument about the things they have kept from each other, and James ends their friendship.
Lynsey's doctor reluctantly agrees to sign her redeployment waiver. She is unable to reach James, but discovers he had the truck repaired for free, and is inspired to reconnect with Justin, visiting him in prison. Changing her mind about leaving, she is able to bring herself to clean her mother's own disused pool, and to swim at a public pool. She visits James and urges him to ask her to move in again, hoping to make amends with her friend, and to build a life where support and understanding replace the isolation that trauma once brought.
