Michael Frayn's Spies reads like Mark Twain's The Adventures of Tom Sawyer with the Mississippi setting replaced by an English setting. And instead of Tom and Huck witnessing a murder, Stephen and Keith believe that Keith's mother is really a German spy during wartime.

The story begins with Stephen as an old man. He makes a return trip home to England, bent on remembering why and how the familiar smell of something he cannot recall stirs so much emotion inside him. The story is of him seeing himself as a boy in late June. He walks the streets of his old neighborhood, following the memory of his younger self and recalling the way he and a friend spent those particular summer months…

In a neighborhood where families treat children like art — seen and not heard — Stephen enjoys spending more time with Keith's family than his own. Keith's mother treats him like a person. And even though Keith's father never addresses him personally (nor does he even acknowledge Stephen's presence), the boy enjoys seeing the father-figure at home, working in the garden or the garage. It isn't that his own family is mean or neglects him; they are just dull compared to Keith's. His own father is always so busy with work, vanishing all day long and returning exhausted at night with just enough ambition left to snooze in the parlor chair.

One day Keith drops a bomb. He tells Stephen that he believes his mother is a German spy. Stephen automatically believes his best friend's allegations without question, and they dedicate their days and evenings to spying on her. Though the mother acts suspiciously at first, their game is only built on circumstantial evidence.

Keith's mother makes multiple trips each day to visit her sister who lives just a few houses down. From there, she always heads toward the market. She also makes several trips a day to the post office to mail a multitude of letters. But why would someone go to market and to the post office more than once a day? Keeping a good distance behind, the boys plan to follow her in order to answer that question.

Their spying quickly uncovers more than they could have imagined. Keith's mother is not going to town. She is headed somewhere else, somewhere more secretive. The boys find a hidden box by the railroad tracks with peculiar items locked away inside, and always the mysterious mark of the letter "X". Soon, though, their game of spying on Keith's mother gets out of hand, and Stephen finds himself sucked into a dark tunnel of inner turmoil because he's found out more about Keith's family than anticipated. Sharing the information with his best friend will only make things worse, but keeping things a secret is ruining their friendship. And in the midst of it all, Stephen thinks he might know the truth, though is perhaps too young to grasp what the truth actually means.

Keith's mother is on to their spying and lets Stephen know that his behavior is not acceptable, and that she does not appreciate being followed. She entrusts him to bits of more truth, letting him know exposure could turn out to be quite dangerous. It is when Stephen keeps at the charade that he learns the whole truth, and only then does he understand the unraveling he has caused.

Poetic narrative and flowery description give this intriguing mystery novel flavor and flow. Every question that's asked is answered. Frayn's story is about many things: friendship, adultery, war, neighbors, dreaming and honor, making Spies a unique coming-of-age story. It is not a fast-paced mystery. It is not a hard-boiled thriller. But it is a mystery filled with tension and some eerie scenes. It is an easy book to get into, and a hard book to put down. Was Keith's mother really a German spy? Does it really matter one way or the other?