In this horror thriller from director Adam Wingard and screenwriter Simon Barrett (You're Next), an unsuspecting family contends with a series of bizarre and unexplained deaths after opening their home to a soldier (Dan Stevens) who swore he'd look after them after seeing their son killed in combat. When David (Stevens) shows up on the Peterson's doorstep claiming that he was with fallen soldier Caleb Peterson as he took his last breath, grieving mother Laura (Sheila Kelley) and her husband Spencer (Leland Orser) invite him to stay with them as he makes the transition back to civilian life. Meanwhile, Caleb's sister Anna (Maika Monroe) begins to sense that something isn't quite right about David. Sure David has helped her misfit brother Luke (Brendan Meyer) stand-up to some ruthless local bullies, but when a furtive inquiry into his past raises more questions than it answers, Ann grows convinced that he's harboring some very dark secrets. Those suspicions seem to be confirmed when her boyfriend is accused of murder, and her father's boss perishes under bizarre circumstances. Later, when a military official (Lance Reddick) shows up in town with a small army of mercenaries, Anna's worst fears are confirmed as al hell breaks loose, and her once-peaceful town becomes an all-out war zone.