Mission to Venice is a 1964 French-Italian-West German film starring Sean Flynn loosely based on a novel by James Hadley Chase and directed by André Versini.
Michael Newman (Sean Flynn) is asked by the wife of a friend of his father to help search for her missing husband.
In Venice Michael meets an icy blonde (Karen Baal) and her "husband" who know something about the missing man.
After some harrowing experiences, where a girl is murdered, the missing man is found tortured half to death.
The man who was not actually the husband of the icy blonde turns out to be leader of the spies and tries to get the document proof from Newman.