Talking to strange men - Ruth Rendell

Safe houses and secret message drops, double crosses and defections - it sounds like the stuff of sophisticated espionage, but the agents are only schoolboys engaged in harmless play, unaware of the danger awaiting them if their messages were intercepted...

John Creevey doesn't know the truth behind the mysterious codes he is reading. To him, the messages he decodes with painstaking care are the communications of dangerous and evil men. As he comes face to face with the reality of his beloved wife Jennifer's defection, he begins to see a way to get back at the man she left him for, a man with a disturbing connection to schoolboys...

And soon the schoolboys are playing more than just a game.