While aboard the cruise ship Lurleen, Alvin unknowingly assists a jewel thief in stealing some jewelry. Believing he was doing a good deed for a lady, he rushes to tell Dave but is hit with the news it was stolen. While Simon and Theodore investigate the crime, they find fingerprints and chipmunk hair that led them to Alvin. When they confront Alvin, he tells them what happened and the boys make a plan to catch the thief. Meanwhile, Dave is questioned by the detective for being found in the victim's room. Their plan doesn't go as hoped, but they capture the thief nevertheless.
- Simon gets the pleasure of playing Sherlock Holmes, while Theodore gets to play Holmes' assistant, Doctor Watson.
- The book The Chipmunks' Cruise is based off this episode.