Spioonid - Michael Frayn

Stephen, the main character of the novel "Spies", returns as an old man to London, where he lived as a child, and recalls the events of the Second World War there. The ones that happened after Stephen's best friend Keith announced that his mother was a German spy to be spied on. Little did either of the boys know, as they secretly watched Keith's mother's daily activities, they would discover terrible secrets that would change their lives forever.