Erin accompanies her boyfriend, Crispian Davison, to his family reunion at their vacation home in rural Missouri. Present are Crispian’s parents Aubrey and Paul, Crispian’s older brother Drake and his wife Kelly, Crispian’s younger siblings Felix and Aimee, and their partners, Zee and Tariq, respectively.
During dinner, someone shoots crossbow bolts through the window, killing Tariq and wounding Drake. The survivors discover that their cell phone reception has been jammed. Aimee runs outside for help but runs into a garrote wire which slices her throat, killing her. An intruder wearing a fox mask kills Aubrey, leaving the words “you’re next” in blood on the wall.
Erin texts 911 and searches for weapons. Another assailant in a tiger mask attacks her but she escapes by stabbing his hand. Kelly discovers Fox Mask, panics and flees the house, only to be killed by an attacker wearing a lamb mask. Crispian leaves the house to look for help. Tiger Mask attacks Erin with an axe but she kills him.
Paul finds sleeping bags and food wrappers that indicate the killers have been staying in the house for some time. Fox Mask kills him. It is then revealed that Felix and Zee hired the assassins to murder the family so they could collect their inheritance. Lamb Mask finds Tiger Mask’s corpse and flips the dinner table over in rage. He discovers a wounded Drake hiding, but retreats after Erin stabs him with a screwdriver. Erin sets up nail traps by the house’s entrances, explaining to Zee that she grew up in a survivalist compound where she learned combat and survival skills. Felix kills Drake.
On the upper floor, Erin comes across Paul’s body. She jumps through a window to escape Fox Mask, injuring her leg. Lamb Mask is injured by one of her nail traps. While hiding, Erin overhears an argument between Felix, Zee, Fox Mask, and Lamb Mask. Her cell phone beeps to indicate that her text to 911 has gone through, alerting the killers. She is able to ambush and kill Lamb Mask.
Realizing she cannot outrun Fox Mask with a wounded leg, Erin sets a trap at the front door. Fox Mask enters through a window, so Erin kills him in the basement. Zee and Felix attempt to kill Erin themselves, but she kills them with a blender and knife. Felix’s cell phone rings and Erin answers without speaking. Believing he is speaking to Felix, Crispian reveals his involvement in the scheme. Erin confronts him when he returns, and Crispian explains that she was never meant to be targeted. After he attempts to bribe her into staying quiet, she kills him in disgust.
A police officer arrives and shoots Erin in the shoulder, having seen her kill Crispian. After calling for backup, he attempts to enter the house and falls victim to Erin’s front door trap.