The Man Who Was Lucky

First published as Date In The Dark in The American Magazine (Dec. 1935) then in 3 issues of The Saint Detective Magazine (US - Mar. 1955, AUS - Mar. 1955, & UK - May 1955) with the current title. Also published in the collection The Happy Highwayman and The Saint Two In One.
A gangster has vowed to kill a witness against him. The Saint says otherwise.