This is one of my favorite Cate movies and among my very favorite movies ever. Matt Damon plays Tom Ripley. In New York Tom is hired by the rich father of Dickie Greenleaf to go to Italy find Dickie and bring him home. In Italy Tom falls in love with Dickie's lifestyle--er--life. So, yeah, Tom's a psychopath. Cate plays Meredith Logue, also American, also rich. She falls for Tom, but thinks he's Dickie so she causes problems.
Cate has a very small role in this movie. She has roughly 4 scenes. But that doesn't mean you shouldn't see this film. Cate was nominated for a BAFTA as best supporting actress for this role.