Thirteenth in the long-running mystery series with Dr Launcelot Priestley.

When a dead body was found at the foot of Tilling's Folly - the lighthouse-like monument on Brown Ridge - under circumstances which precluded the possibility of suicide, Inspector Richings thought it was high time to summon the aid of Scotland Yard. For some months past a series of robberies in his district, all apparently committed by the same gang, had completely baffled him. When a clue, concerning a mysterious gray car which had been connected with the other crimes, turned up again, he was at his wits' end. And that is why Inspector Hastings and Dr. Priestley appeared on the scene.