Aron, a Marine veteran of Afghanistan, is haunted by his failure to prevent the death of his closest friend Jay and constantly reminded of his loss by a wounded ear and tinnitus sustained in his attempt to save him. His fiancée, Alyssa, a physician's assistant, insists he try prolonged-exposure therapy, and with her support, the encouragement of a college instructor and AA, he finds the strength to visit Jay's family in Utah, confess his failure and accept a hard truth.
Aron has made considerable emotional progress and given up alcohol, but is unable to find work because of the Recession and is hungry for stimulation and camaraderie when Kane, his closest surviving fellow Marine, visits with an offer of employment with a team led by two former SEALs.
Whit, funder and second in authority, comes to interview Aron and is impressed by his physical excellence, athletic achievements, unassuming disposition, naïveté and concern for the environment.
Neil, the handsome, charismatic and somewhat sociopathic leader, comes for a second interview, is similarly impressed and insists Aron demonstrate his exceptional marksmanship.
Aron flies to Phoenix to join the team, which now includes Kurt, a troubled teenager. All five have had absent or abusive fathers, feel betrayed by politicians, alienated by corporate destruction of our environment, abandoned by the economy, and find a sense of belonging and self-value in their bond. Aron melds with the team during a roughhouse basketball game and a paint-ball battle against a team of tough former servicemen led by Stan.
Neil, a skilled manipulator with few scruples, pulls Aron into deeper commitment and reveals his objective: the team will become eco-warriors and target men responsible for the environmental damage caused by fracking, (He doesn't mention that they will be extorting money to fund and expand future operations.) Aron is offered a ten-thousand-dollar bonus for slightly wounding an offender.
Aron is reluctant to commit a crime and looking for an opportunity to escape until Alyssa informs him she's pregnant and he feels they will need the money to start a family. He slightly wounds their first target in Breckenridge, Colorado, and Neil immediately finds another in Vail. Guilt-stricken and homesick for Alyssa, Aron demands a leave of absence, which he intends to extend to a total break.
Back home in Garland, a suburb of Dallas, Aron is visited by FBI Agent Barton, who offers him exemption from prosecution in exchange for cooperation in bringing down the team. Aron refuses, and he and Alyssa quarrel.
Kane calls Aron with a plea for help and news that Stan's gang – hired by their first target – is determined to gun down the team. Alyssa refuses to shelter Kane, and Aron takes him to stay with his down-to-earth widowed mother, a cook at a local cafe, in his boyhood home in the country.
Kurt comes begging for refuge and help for Neil, who has been wounded. Kane finds a nearby vacant house in which they hide, and while attending to Neil's wound Aron is pulled back in.
Stan's gang tracks them down electronically, but underestimates the team's weaponry, and during a failed assault Stan and two members of his gang are killed. Whit is mortally wounded, Neil stays with him to delay pursuit by the police, and the others escape.
