A London business man (and former World War II colonel) surprises a young burglar who proves to be none other than his bravest wartime subordinate. Convinced that the fleeing "intruder" merits salvaging, the ex-colonel stalks him, contacting their scattered comrades-in-arms to learn what made a gallant soldier into a post-war derelict. This novel was made into the 1953 film "The Intruder."
Another excellent short novel from Robin Maugham featuring a frmer tank soldier as protagonist. This one concerns the discovery that a former comrade, Ginger, has fallen into crime and the search to find out why. During this search, our protagonist finds out just as much about himself as he does about Ginger.