The Smart Detective

Written by Leslie Charteris

Copyright 1940

First published as The Saint and the Siren in The American Magazine (Jun. 1936) then in 2 issues of MacKill's Mystery Magazine (UK - May 1953 & US - Jun. 1953), 3 issues of The Saint Detective Magazine (US - Nov. 1954, AUS - Jan. 1955 & UK - Mar. 1955)  and The Saint Mystery Magazine (UK - Mar. 1962) with the known title. Also published in the collection The Happy Highwaymanand The Saint Two In One.
Simon Templar has taken a shining to some emeralds that a bad guy has but he does not know a detective is shadowing him.