In a seemingly ordinary and warm night, a lamb mask is creating a haze of killing. At any time, anyone may become the next target of the masked killer. Young Irene (Sharni Vinson) is returning to her Missouri holiday home with her boyfriend Crispian (AJ Bowen) to attend his parents' wedding anniversary. Crispian's brother and sister both brought their other halves to the party, and the family was having fun at the dinner table. However, outside the house was another creepy scene, with several masked killers eyeing the family. Suddenly, his younger brother Drake was shot in the back, and the killing started quickly, and other family members were frightened and injured one after another. At this critical moment, Irene took over, organized the family's defense, and burst out with an amazing survival instinct. The holiday home instantly became a bloody battlefield of life and death...