While on a weekend trip, a group of friends are forced to seek shelter inside an abandoned prison where a nun named Sister Monday had once been assigned. During her time at the prison, Sister Monday was suspected of killing prisoners who were serving out their sentences but before she could be questioned, she disappeared. Once inside the prison, terrifying childhood memories and family conflict come to the surface for the group where they are forced to face their fears. Don't CROSS Sister Monday. She will PREY for you.