Natalie is taking a break from studying for her PI license, the last step to becoming Monk's full partner. She sneaks off to Half Moon Bay for a retreat run by Miranda Bigley, leader of the Best Possible Me self-help program, but her plans for a relaxing weekend are disrupted when Monk tracks her down to rescue her from the 'cult.' Their argument is cut short when Miranda, in full view of everyone, calmly walks to the edge of a cliff and jumps. Even though Miranda's death looks like suicide, Natalie is sure it's murder. But Monk brushes her off to help the SFPD solve the murder of a clown, despite his coulrophobia. As Monk and Natalie begin their independent investigations, they quickly learn that if they want to figure out whodunit, they will have to find a way to become true partners.

Of all the things that make Adrian Monk uneasy, change ranks high on the list. So when Natalie completes her P.I. license-and technically becomes Monk's boss-it's not easy for him to accept. Nor can he accept Natalie attending a business seminar at sea without him, even if it means spending a week with her on a cruise ship. Between choppy waters and obnoxious kids, Monk finds himself in a perfect storm of anxiety. Luckily, Mariah, the cruise director, is always able to smooth things over. Until someone pulls the man overboard alarm, the ship drops anchor and the crew fishes Mariah's dead body out of the water. Finding alcohol in Mariah's system, the ship's doctor declares her death an accident, but Monk isn't convinced. He knows that Mariah and the captain were having an affair. Could someone have pushed her overboard? When the captain hires Monk and Natalie to look into a mysterious rash of vandalism onboard, Monk steers the investigation toward murder?