When Mr. Leon, a new upstairs neighbor, receives some deliveries late at night that appear to be a coffin and a cannon, Martin is suspicious. He meets Mr. Leon and finds out that he wears a wig, sunglasses, and gloves, and becomes certain that their apartment building is harboring a spy. Then Mr. Leon asks Martin to walk his dog, providing the perfect opportunity for some spying of his own. Despite a too-neat ending--all mysterious behavior is explained away--the story is entertaining and well-written, a step above the usual easy reading fare. Unzner provides endearing color illustrations on every page of this amiable book.