Mr. Monk and the Big Reward

S4, E13: Monk and Natalie go to police headquarters to ask Captain Stottlemeyer for a raise. While they are there, Lieutenant Disher brings in Warren Landis, a security guard from a local museum, for questioning. The world-famous Alexander diamond has been stolen from the museum, and the police are interrogating all museum employees. When Monk notices some chemical residue on Landis' fingers, Disher arrests the security guard on drug charges. When Natalie hears that there's a million dollar reward for the diamond, she convinces Monk to use his detective skills to try to find the stolen gem.