The Melancholy Journey of Mr. Teal

First published as The Kidnapped Killer in The Thriller (August 8, 1931), then in 2 issues of The Saint Mystery Magazine (US - Sept. 1962 & UK - Feb. 1963) with the known title. Also published in the collections The Saint vs. Scotland Yard and Saints Alive.
Having almost enough to retire, Templar goes after two diamond smugglers but things go terribly wrong.