Contrary to common belief, not all Carr/Dickson's books involve impossible crimes. This one is more a mixture of the bizarre (a policeman reports looking through a window to see lights moving round an upside-down flowerpot!) and farce (H.M.'s sidekick Ken Blake is sent off on a quest which involves impersonating first a policeman and then a clergyman). The denouement is fairly clued but I'd be surprised if many people could guess it. ( )