A man's body is found on the Embankment missing a canine tooth, which turns up nearby on the ground. It is the first in a chain of grotesque murders that all involve the same M.O.; though on subsequent occasions, the tooth has been taken. Out of his depth, Detective Inspector Evens of Scotland Yard calls in London's foremost amateur criminologist, Professor Barrington. What is the connection between the murdered men - and can Barrington bring the criminal to justice before he himself is added to the tally of the dead?