As his wedding day approaches, a nervous groom reluctantly joins his childhood friends at a wild bachelor party organized by his overbearing best friend. However, the festivities turn into a night of terror when a psychotic killer starts hunting them down, forcing the group to confront their deepest fears and fight for their lives in a desperate struggle for survival.

After becoming injected with a formula derived from an alien ship, a lab gorilla escapes from his containment and befriends two young boys. The alien formula causes the gorilla to grow to gargantuan size and rampage throughout the city and the boys must find a way to save their simian friend before the army takes him down.