The Ringer by Edgar Wallace (Pan, 1957)

More Edgar Wallace.  This one was found in The Green Shed:

 

THE RINGER, considered by many Wallace 'fans' to be the best of his thrillers, tells of a killer known by this name, whose exploits had terrified London--such a master of disguise that the police had never been able to circulate a description of him.  Mixed up with the Ringer was a tricky lawyer of Deptford, Maurice Meister.  Now young Detective-Inspector Alan Wembury is taking over the Deptford police division, and is hoping to marry Mary Lenley, who has recently become Meister's secretary.  News comes that The Ringer, who had been traced to Australia and was reported dead, is back in London.  Meister will be his next victim, for he left his sister in Meister's charge and her body was found in the Thames.  Soon a gaunt stranger is shadowing the frightened lawyer, who seeks police protection. Wembury is involved in an affair of extreme difficulty, complicated by the fact that Mary's brother, ruined by association with criminals, is jailed for robbery--and Meister knows more of this than he will admit.  Moreover, the unpopular, bearded Inspector Bliss, just returned from America, is working along his own lines to solve the problem.  Who is The Ringer?  It will be a clever reader who can spot him before the very end of the story.

With a summary that detailed, it's hardly necessary to read the book!  And given we're talking about Edgar Wallace here, probably just as entertaining.  Just skip to the last chapter to find out who actually was The Ringer.

(Edgar Wallace was a best seller in his day, but his books have dated woefully.  However they were reprinted often--well into the middle of last century.  Delightful paperbacks like this one turn up quite regularly on charity stalls and in junk shops, so expect to see a few of them featuring on my blog!)