I just remembered another favorite - The Mask of Demetrius - with Peter Lorre, Sydney Greenstreet and Zachary Scott. Lorre, a mystery writer, becomes fascinated by the story of Demetrius Makopoulos, after DM is found dead. He traces DM's path through Europe, trying to find out more about him, with Sydney Greenstreet along for the ride as a shady character who has reasons of his own to find out more about DM. It's a good mystery, and a lot of fun, too. I'll watch anything with Lorre and Greenstreet in it.