The Buntings are an elderly London couple who have fallen on hard times. They take in a lodger with the strange name of Mr. Sleuth, who pays handsomely for their shabby rooms. He seems to be a perfect gentleman but none the less they begin to suspect that he may be the Jack-the-Ripper-like serial killer known in the press as 'The Avenger'. As the number of murders in the city begins to mount, and ...