A young American woman, Mina, lives in Galway, Ireland, and works in a pet store. She goes to deliver a parrot to a zoo near Belfast, and soon the car breaks down in the middle of a dense forest. As night approaches, something terrible is looming, and Mina finds refuge in a strange glass-walled house where three people live. They have to follow certain rules to avoid being caught by the so-called caretakers - monsters who come to watch them every night.