Harvey Disher - Lt. Disher's uncle - is lovingly feeding and primping his pet pig Nadine on his quaint California farm, when Harvey's neighbor, Jimmy Belmont, shows up. The two men are having some sort of dispute, and Jimmy Belmont offers Harvey a healthy amount of money to resolve the situation. Harvey rejects the offer, and Belmont promises to clear things up soon.
Later that night at the local square dance, everyone, including Jimmy Belmont, is dancing and enjoying the merriment when the lights begin to flicker. As the lights turn back on, Belmont asks if anyone heard a gun shot. The townsfolk say no, but the town's sheriff, Margie Butterfield, is concerned, and leaves the square dance to investigate. As she drives near Harvey Disher's farm, she sees Nadine the pig lying in the middle of the road, dead. Just down the road, she finds Harvey Disher's truck at the bottom of a hill. The truck has crashed into an electric fence, and as she gets closer, she finds Harvey Disher's body, dead of an apparent self-inflicted gunshot wound to the head.
Meanwhile, back in San Francisco, Lt. Disher has decided to resign from the police force after botching a big drug raid. Capt. Stottlemeyer tries to persuade him not to quit, but it's no use. Uncle Harvey left Randy the farm after committing suicide, and Randy has decided to move to the country to start a new life.
On the farm, Randy has reservations about the death of his uncle. He calls Monk, and asks if he would come to the farm to investigate. Monk, of course, has reservations of his own. Monk can't possibly go to a farm with animals, nature, and - worst of all - dirt. But after a little coaxing from Natalie, Monk decides that he should help his friend Randy, and the next day he's on a bus to the country.
When Monk arrives, he meets Oates, the farm's reliable farmhand. Oates takes Monk to Randy, who is sound asleep and listening to a compact disc of a motivational speaker. They wake him up, and the three men set off to the scene of Harvey Disher's accident.
Harvey's truck is still there - Randy has been careful not to move it. Monk considers the current explanation: Harvey accidentally ran over his beloved pig and became so distraught that he killed himself. Randy points out that Harvey shot himself with a rifle from the truck's locked gun rack, which is strange considering there was a hand gun more conveniently located under the truck's front seat. In addition, Nadine somehow escaped from her pen, despite the fact that she wouldn't let anyone except Harvey near her.
Shortly thereafter, Sheriff Butterfield and Deputy Hatcher show up and weigh in on the situation. The Sheriff is positive that Harvey Disher's death was a suicide. The night of the accident, she and her deputy arrived on the scene soon after Jimmy Belmont heard the gunshot, and there wasn't a soul around. But Monk isn't convinced. How could Belmont have heard the gun shot? The dance hall must have been noisy, and it's a solid half mile away from where Harvey Disher died. Disher and Monk decide to perform a test at the next square dance, which is scheduled for later that night.
At the square dance, Monk asks around, but nobody but Jimmy Belmont heard the gunshot the night Harvey died. Monk glances at his watch. It's almost time for their test. Over at the crime scene, Randy points his gun in the air, pulls the trigger, and then realizes he forgot to load the weapon. He's messed up again. Monk is near a window, waiting to find out if he can hear the noise, but it doesn't happen.
Back at the farm, Randy is devastated with his poor performance. Oates tries to be encouraging, but it doesn't work. Despite the failed test, Monk is becoming convinced that Jimmy Belmont was involved in Harvey Disher's death. The three men devise a plan. The following morning, Monk will head to Belmont's farm and pose as a Spanish-speaking farmhand looking for work.
The plan works. Belmont hires Monk, and puts him to work right away. Monk tries to extract information from the other workers, but Monk's Spanish is poor, so he barely understands a word they are saying. Monk decides to go off exploring, and finds a heavily fenced-off area. As Monk tries to get a look behind the fence, Jimmy Belmont shows up with a gun. Jimmy knows that Monk is a detective. But Monk knows Jimmy's secret as well. Jimmy has been growing marijuana in the fenced-off area. Harvey must have threatened to report it to the police, and Belmont killed Harvey rather than get rid of the illegal crop. But Monk has no proof, and Belmont threatens to kill Monk if he doesn't end his investigation.
Hours later, Belmont returns to the fenced-off area. Monk has followed him, and watches as Belmont begins burning away his marijuana crop. Monk tries to take some pictures, but he's soon overcome by the marijuana smoke.
Afraid of the effects of the marijuana, Monk runs back to Disher's farm in a panic. As he rants and raves to Oates about the side effects surely to take hold, the farm's sprinklers come on. And just like that Monk sobers up. And just like that, Monk has solved the case.
Monk rushes back to the house, and prepares to call the Sheriff. But Oates has a better idea. Minutes later, they go into Randy's room, where they find Randy sound asleep and listening to his motivational CD. Monk turns off the CD and begins whispering those famous words into Randy's ear: "Here's what happened..."
The next morning, Monk and Oates are eager to see if their plan worked. Disher enters the kitchen, groggy and half asleep. They ask if he has any new thoughts on the case. They wait, and wait some more. And then eureka! Disher's got it!
They all drive to the scene of the crime, where they meet Sheriff Butterfield, her deputy, and Jimmy Belmont. Disher breaks down the solution to the case. Belmont killed Disher's Uncle Harvey over the marijuana. Belmont lured Harvey to the scene of the crime, shot him, then set up Harvey's body in the truck to make it appear to be suicide. But Jimmy Belmont needed a motive, so he killed Nadine the pig, and left her dead body in the middle of the road. Then, Belmont propped up the rear fender of Harvey's truck on some salt licks, high enough so the truck's rear wheels were off the ground. He turned the truck on and put it in "drive," so the rear wheels started to spin. Belmont then left and went to the town dance hall, knowing that the sprinklers would go off later, and melt the salt licks while Jimmy innocently attended the square dance. Once the licks melted, the truck's tires would hit the road, thus sending the truck over the pig and into the electric fence, causing the minor blackout at the dance. When the people from the dance responded, they would find Harvey Disher crashed into the fence, dead of a self-inflicted gunshot. It was a perfect plan, except for Disher's brilliant, Monk-aided revelation.
But there's still no physical evidence to connect Belmont to the crime. Then, Disher has a real moment of revelation. Jimmy Belmont would have been the last person to handle the truck's key, which is still in the ignition. Disher goes to the truck and takes the key, which has a fingerprint on it. If that fingerprint belongs to Jimmy Belmont, that would mean that Jimmy was the last person to operate the vehicle, not Harvey. It's the final piece of evidence needed to put Jimmy Belmont away.
Having "solved" the case, Disher decides to leave the farm and return to the San Francisco Police Department with his new found confidence. Capt. Stottlemeyer is happy to have him back, admitting that he never submitted Disher's resignation papers in the first place. It's a fine moment for Monk. This time, he did more than just solve the case. He gave a friend his confidence back.