"Lady of Vengeance" from 1957 could have been better, yes, but it is what it is -- one of those "B" British films that can be kind of fun.
This one stars Dennis O'Keefe, who made several of these types of films.
Dennis O'Keefe plays a newspaper mogul, William Marshall, whose ward (Eileen Elton) committed suicide. He receives a letter from her after her death that tells the story of what led her to such a drastic act.
Marshall approaches a stamp collector named Karnak (Anton Diffring) in order to get his help in committing a murder, on one condition: the victim must suffer a slow, painful death.
In other hands, this might have been terrific; here it comes off as average, due to a distracting subplot and the fact that the script could have been tighter.
Most notable about this film is the performance of Anton Diffring, a striking actor both in looks and persona, who worked in character roles in films in Britain, Germany, and in international films such as Fahrenheit 451. He died in 1989, possibly from AIDS. He gives a marvelous performance here and it's easily the best thing about the film.