Jack, a builder, meets Penny, a maths professor, on a computer date. Somewhat daunted by her status, he agrees to go on a walk with her rambling group. The rendezvous is at Forest Gate station. The plan is to hike across Wanstead Flats, heading north, on to Epping Forest. Just a walk, what could go wrong with that?

Except Nova, Jack's ex, is one of the ramblers too, and not pleased to see him. The day may have improved if Mike, the walk leader, had not been quite so severe. All in all, it is an ill-assorted group that sets off on Saturday morning for a 13 mile hike. Is it really a surprise when one of them is murdered?