When Monk witnesses a Chinese gang murder, he becomes a federal witness under the protective custody of old friend Agent Grooms. Grooms takes Monk, along with Natalie and Captain Stottlemyer, to a remote FBI cabin in the woods. On the way to the hideaway, they meet Martin and Kathy Willowby, who live in a cabin not far from the one where Monk is staying.
Meanwhile, back in San Francisco, Lieutenant Disher is dating a beautiful Chinese woman named Hayley. They begin frequent Hayley's favorite Chinese restaurant together, and at the end of every meal they always have fortune cookies. Soon, something strange starts to happen: the fortunes in Lieutenant Disher's cookies begin to come true!
Back at the FBI cabin, Monk is having a difficult time getting acclimated to the outdoors, and when night falls, he can't fall asleep. Suddenly, he hears a man's voice crying out. When he gets out of bed to take a look, he sees the lights in the Willowby cabin flicker on and off. Monk suspects foul play, and the next day he sees Kathy Willowby behaving oddly: she buys bags of ice, she buys a new radio, and Monk hears country music blaring from her cabin despite the fact that her husband hates country music. Monk, Natalie, and Captain Stottlemeyer decide to investigate, so they lock Agent Grooms in the bathroom, steal his vehicle, and head for the Willowby cabin. Unfortunately, they get stranded overnight in a horrible thunderstorm.
The next day, back in San Francisco, Disher gets a new fortune: "An old friend is in danger. Only you can save him." He immediately assumes the fortune is referring to Monk, so he sets out for the FBI cabin to try and protect his friend. But what Disher doesn't know is that the whole business with the fortune cookies has been a set-up: Hayley has been working with the Chinese mob to try to figure out Monk's whereabouts so they can bump him off - and now Disher is going to lead them right to him!
Back in the woods, Monk, Natalie, and Captain Stottlemeyer have finally come across the Willowby cabin, where Martin Willowby's dead body is being pulled out of a fishing boat. According to the local police, Martin was struck by lightning while fishing during the storm. Monk, however, has a different theory: murder.
Before Monk can make his case, Lieutenant Disher shows up. He's been followed by Chinese gunmen, and soon the assassins are riddling the cabin with bullets in an effort to kill Monk. During the shootout, Monk explains that Martin Willowby was killed by his wife: first, she electrocuted him while he was taking a bath by dropping a radio in the tub; then, she preserved the body with ice while waiting for the lightning storm to come; and finally, when the thunderstorm came, she put Martin's body into the fishing boat, cut it loose on the lake, and then reported his death as an accident.
It's another mystery solved by Monk - but while he's being shot at by Chinese gunmen! Fortunately, Agent Grooms arrives just in time to stop the shooters. Thus, after an especially dangerous adventure, Adrian Monk emerges victorious over crime once again.