Lady Of Vengeance.

William T. Marshall (Dennis O'Keefe) finds it in a letter he receives from Melissa Collins (Eileen Elton) asks him to take revenge on her lover, philandering musician Larry Shaw (Vernon Greeves), who caused her such pain he made life not worth living. Marshall hires criminal mastermind, Karnak (Anton Diffring), an avid philatelist, to plan the murder of Shaw.