A group of students is on a field trip to an ancient castle when a storm erupts. As they are about to leave, four friends are cornered by the class bully, who tries to pull one of his usual pranks. Instead, they all get the scare of their lives when they fall down a tunnel that takes them into the future: a future where mankind has nearly disappeared from the face of the earth, and where nature has taken control. The friends will have to face up to this hostile new world—as well as their nemesis—if they're to have any chance of making it back home...