Right after Mark's next-door neighbor is murdered, he gets a new neighbor-the beautiful but mysterious Sylvia, who has just arrived from London. Mark is drawn into a mutually obsessive relationship with Sylvia. She is secretive regarding her past and Mark's friends caution him that she can't be trusted. But Mark won't listen to his friends or to the priest who later claims that Sylvia is a deadly threat.

Mark is enchanted by Sylvia's beauty and charm, even though dating her has its challenges. Whether it's performing gymnastics on the ledge of the Golden Gate Bridge, creating an embarrassing scene at the wedding of Mark's best friend, or shocking Mark with her unusual sexual proclivities, Sylvia never misses an opportunity to make a bad first impression.

When Mark first meets Sylvia, he tells her, "You're the girl of my dreams!"

Sylvia smiles and responds with a warning-"Be careful what you wish for."