This 4th book in the Tommy Hambledon series, though first published in 1943, is set in 1938 before WW2 has begun. Hambledon doesn't enter into the story for a surprisingly long time, the narrative being told primarily from the perspective of Jim Warnford. Warnford & Marden are operating "without lawful authority" and each man has his own reason for not wanting to bring the police or British Intelligence in on the action.

Once the action gets going, there is plenty of it & the final scene at a well-respected lunatic asylum in the country being used by German agents was almost too 'over the top'! Such fun! ( )

Although Hambledon is eventually involved, this actually focuses originally on a man named Warnford who had been dismissed from the Tank Corps unjustly on suspicion of espionage when new tank plans are stolen and sets out to clear his name with the aid his faithful batman and an unlikely gentleman burglar --some of the wildest adventures in the series. ( )