When English teacher Beth Landow falls from the clock tower at Trudy's former high school, Monk is called in and quickly disproves the police theory of suicide. The trail of clues leads to a science teacher but he has an iron-clad alibi. Monk becomes a substitute teacher in the hopes of solving the case.
A skydiving student on spring break appears to have drowned in midair - a case strange enough to convince Monk to travel to Mexico to investigate. While there, he must deal with a myriad of phobias, the theft of his luggage, the shortage of his favorite brand of bottled water, and apparent attempts on his life, all while trying to unravel one or more murders that are not what they seem.
When a powerful CEO and his wife are shot to death in a deserted parking lot, the police investigate the husband's enemies. But Monk thinks it's all about the wife and the affair she was having with a handsome young ballplayer.
The world's oldest man dies the day before his birthday, and everyone but Stottlemeyer's wife, Karen, thinks it's just the result of old age. Karen enlists Monk's help to figure out what really happened.
When Randy's mother marries a guy much younger than her he gets worried. When they go to some kind of couples retreat, he asks Monk and Sharona to go and keep an eye on her. So to go in they pretend to be married.