S5, E12: Monk and Natalie are on a visit to Natalie's parents' house, when the conversation turns to their neighbor, Paul Buchanan. Paul grew up with Natalie and has long harbored feelings for her, but Natalie thinks he is a creep. Natalie's parents explain the circumstances of the recent deaths of Paul's father and stepmother. When Monk questions some of the facts of the story, Natalie suspects foul play. She has a hunch that Paul Buchanan is somehow involved, and hires Monk to look into it.