Mr. Monk and the Captain's Marriage (S04E12)

Monk and Natalie join Captain Stottlemeyer at a junkyard to investigate the murder of a small-time drug dealer named Chicklet. While Monk looks around, a cocky young police sergeant named Ryan Sharkey implies that he's having an affair with the captain's wife, Karen. Stottlemeyer punches Sharkey in the face, and then leaves in a huff. Karen emphatically denies having the affair. The captain, still suspicious of Karen, asks Monk to follow her and find out whether or not she's having an affair. (iTunes)