The book starts with an old man literally walking back down memory lane to his childhood. As he walks down his old cul-de-sac he can recall with exact detail the same street in the war with the blackout blinds and the bombed out house.
the narrator comes from one of the more shambolic households down the street and recalls a friendship with the more upmarket Keith. The boy dominates the friendship and it is Keith who starts the ball rolling that leads to the events that the old man has come back to recall.
The words “my mother is a German spy” sets them spying, recording everything in a log book and inventing all sorts of potential spying activities for the mother. The result is no doubt going to be awkward and awful. As an adult reader the worst you suspect her of is having an affair but the boys might have guessed right.