When Dave Drayton notices a strange mist on the lake, he does not think much of it. Later, when his son, Billy, his neighbor Brent Norton, and he travel to the grocery store, strange things begin to happen. On their way to the market, they see the army, the local firefighters, and the police heading toward the mist. When he sees this, Brent mentions something about "Project Arrowhead," a secret military plan that no one knows about. When an elderly man runs into the market with a bloody nose, declaring that something is in the mist, the store immediately becomes besieged by otherworldly creatures which the shoppers and employees must battle.