Book #4 in his own series and #8 in the series.
Before the fall of Paris, Papa Pontivy and Captain Newman start to investigate reports of the theft of British officer uniforms from a Paris Hotel. When they find the hotel manager murdered, they know that German spies are disguising themselves with those uniforms. Newman and Pontivy reciprocate by disguising themselves as a German officer and his French chauffeur to infiltrate Hitler's High Command to learn who the fifth columnists are.