Ronald Knox 
Three Taps 

In a gas-lit inn in the countryside a man lies dead. The police, of course, investigate – and so do Miles Bredon and his wife, in the interests of the Indescribable Insurance Company, with which the deceased man, Mr Mottram, had been heavily insured.The culprit is the three gas taps in Mr Mottram’s room, and Miles hopes to prove that his death is suicide. Miles’ old wartime colleague, Police Inspector Leyland, is convinced it’s murder. And the conclusion is as ingenious as it is surprising.