Writing a story that is looking back through the memories and eyes of a child is fraught with danger because there is a thin line between being patronising and dumbing down or alternatively giving the character too much of an adult like insight.
Michael Frayn treads that line fantastically partly helped by the technique of returning occasionally to the present date for a reality check before diving back into the memories.
The fact that as a reader you are often slightly ahead of the plot is not the point because this is really about how a young boy reacts to the atmosphere of living in a normal cul-de-sac in the middle of the war.
His friendship with the affluent and pampered single child Keith is key to the story as a youthful Stephen is led by his domineering friend into believing that his mother is a spy.
Stephen takes the game more seriously than his friend and they follow his mother around discovering not that she is a spy but that she is protecting her brother-in-law, eho has deserted from the air force. The reader realises that long before Stephen does but where Frayn leaves you guessing is with the fallout of such a relationship. The results are a marriage that seems to implode, a friendship that ends and a growing up experience for the main character that he never forgets.
The book is uncomfortable on occasions, incredibly well observed and casts a different light onj a wartime experience. The idea that we all have secrets to hide and things that if watched and logged would appear odd to the rest pf the world is universal and there is a powerful reminder here that it is often the innocent who unwittingly find the guilty.