In the Middle East, Brad Roback, a seasoned sergeant, and his squad vanish during a patrol. Their equipment and vehicles are found abandoned, with no signs of a struggle. Days later, [Brad] and ten of the other twelve missing soldiers turn up unconscious outside their base. When the men awaken at LRMC in Germany, they reveal unexplainable physical impairments: Brad loses the ability to walk, taste, and see in color, and is plagued by frequent, severe headaches that flare with high-pitched sounds.
[Brad] is sent home to his family, where his deteriorating condition creates tension, not helped by his sister Ashley’s blunt boyfriend Gavyn. As hours pass, Brad’s body and mind continue to degrade: he experiences periods of unresponsiveness, seizures, a worsening wound on his right foot, and a gaunter frame as his eyes and tongue swell; his fingernails and teeth yellow, and he begins exhaling a black fluid from his ears, mouth, and anus. In the morning after his return, he is found by his mother, Karmen, ingesting a large amount of salt in the kitchen, having apparently entered the room of his own accord. As his mother heads to fetch his wheelchair from the parlor, Brad returns to his bed and becomes semi-catatonic, stubbornly refusing medical help when his brother Bruce suggests it.
When Gavyn stops by, his blunt comments about Brad’s condition and his relationship with Ashley spark a clash with Bruce. After Bruce steps outside to cool off and argues with their mother in the yard, Brad—who has just killed and eaten the family dog, Fulci—rolls into the kitchen, stands, and attacks Gavyn. Gavyn’s cries bring Bruce and Karmen, who discover him dead from a severe head wound, and Brad convulsing on the floor. As Bruce tries to revive him, Ashley, who has just returned from dance practice, leads their mother out of the room. Once Ashley and Karmen are gone, Brad springs to life, rips Bruce’s lower jaw off, and shuffles after his mother and sister, making animalistic noises.
Brad locates Ashley and Karmen, and murders Ashley by punching through a door and impaling her neck on the splintered wood, then stumbling after his mother as Karmen strikes him with a metal wall ornament. A slug-like creature surges from Brad’s sella turcica, seemingly confirming his earlier, sarcastic theory that he and his squad were abducted and experimented on by aliens. Karmen fights back and defeats both Brad and the entity, but the violence culminates in tragedy: the family is left with home movies of their life together, and Karmen’s husband returns home to discover that she has hanged herself in the garage.
