The nightmare begins when a disparate group of tourists visits an ancient Roman amphitheatre ringed by prehistoric standing stones. The entire group moves backwards in time precisely two hours - and it doesn't stop there. Every few hours or days, they find themselves inexplicably returned to the amphitheatre, having to adjust to yet another backwards shift through time. Each time, one of their nimber is found butchered on the altar stone. Why is this happening? And where will it all end?