The Beauty Specialist

First published as The Z Man in The Thriller Library (Mar. 27, 1937) then as The Saint and the Z Man in Popular Detective (Oct. 1937) and in The Saint Mystery Magazine (UK - Oct. 1964) with the current title. Also published in the collections The Ace Of Knaves and The Saint Two In One.
The 'Z-Man' is a vicious blackmailer and the Saint is suspected of being him.