The Ringer by Edgar Wallace.
First published 1925; cover shown is the 1948 Pan Books (UK) paperback edition. 'The Ringer' was originally published under the title of 'The Gaunt Stranger'.
Edgar Wallace (1875 - 1932) wrote and published over 100 novels. He dreamed up some amazing titles for his thrillers, adventure stories and mysteries, such as: 'The Fellowship of the Frog', 'The Hairy Arm', 'The Man Who Was Nobody' and 'Death Packs a Suitcase'.