The Twenty-One Clues

The Twenty-One Clues is a 1941 detective novel by the British author Alfred Walter Stewart, published under his pseudonym J.J. Connington. It is the fourteenth in a series of seventeen novels featuring the Golden Age Detective Sir Clinton Driffield, the Chief Constable of a rural English county. It was published by Hodder and Stoughton in London and Little, Brown and Company in the United States.

Synopsis
Two bodies are spotted by an engine driver in some bracken close to the railway line. A man and a woman, unmarried to each other and rumoured to have had an affair despite their respectable backgrounds, have apparently taken part in a suicide pact.