It was supposed to be a fun, yet educational trip. It was a chance for the students to get out of the classroom and into the field, to study the local wildlife and ecology, deep in the forests of Snowdonia. For the students, they saw it as a chance to party. But there’s something waiting for them, out there in the woods – a parasite that wants to take control of their minds, to make them do terrible things they wouldn’t normally do. As blood is spilled and the bodies begin to stack up, it is left to just a handful of the students to try and stop this invisible threat that wants them all dead.