Natalie is driving cross-country with Monk, and is mad that Monk didn't talk to any of her friends at a wedding she was invited to reunion. The car breaks down and they pull over on a bridge. They're unable to get a phone signal and Monk walks to the side to try to get a clear transmission and sees a UFO hovering in the sky.
The next day, Natalie and Monk get to a mechanic in nearby Vintonville and Monk asks if anyone has seen any flying saucers in the area. When Monk manages to insult the mechanic, he takes offense and raises his estimate. Natalie tries to convince him to show a little empathy but it doesn't go well.
Natalie calls Stottlemeyer and warns him they won't be making a training seminar. She tells him what Monk claims he saw. Meanwhile, Monk goes to the sheriff's office and hears him talking to a woman about her neighbor Marjorie's disappearance. Once Sheriff Fletcher ushers the woman out while explaining there's nothing to worry about, he takes Monk's statement. Monk is reluctant to say he actually saw a UFO but is finally forced to admit he saw what he thinks he saw. The sheriff promises he'll investigate but is clearly skeptical.
That night, Monk stars seeing imaginary UFOs everywhere as he and Natalie go back to their hotel room. However, Monk sees the UFO, and this time Natalie and the hotel bellboy see it as well.
The next morning, Monk wakes up, looks out the window, and sees a golden alien figure standing outside in the parking lot. He goes back to bed, gets back up, looks outside and sees three aliens. It turns out that avid UFO watchers have arrived in the town, many of them dressed up as aliens like the ones Monk saw. The UFO fans soon fixate on Monk as a primary witness, much to Monk's dismay. They're interrupted when the fans find a potential landing site. Monk and Natalie go along and she wonders if there might have actually been a UFO. Monk is skeptical and acting like himself. The UFO watchers begin to wonder if Monk might be an alien and demand that he show them his belly button. Monk makes a hasty exit and he and Natalie go back to see the mechanic, Boom-Boom. He continues to feign stupidity and Monk half-heartedly tries to apologize.
As the UFO watchers search the desert, they find a corpse. The sheriff finds Monk and asks him to help. They go to the local coroner and examine the corpse of the missing woman, Marjorie. Dr. Garcia confirms she's been dead five years ago and Fletcher explains that Marjorie came into money and dabbled in various hobbies. Monk examines the body and realizes that she's wearing new clothing that don't fit. He finds a silicon packet in her new boots and someone dressed her after she was killed.
They go to see Marjorie's brother, Kyle, who shows them her house. It's filled with knick-knacks. He admits that he wasn't close to his sister. Monk examines the place while Kyle admits that his shop went under a year ago and he's looking for work. The detective finds evidence a rug was in the room and a plastic piece from a new shirt. Monk figures that Marjorie was murdered there. They're interrupted when UFO fanatics show up to watch Monk. When he comes out, they try to swarm him as he goes back to the place in the desert where Marjorie was found. They hear someone park nearby and then the newcomer opens fire. The sniper shoots the sheriff's jeep, wounds Fletcher in the leg and then drives away.
With the radio out and the jeep unusable, someone has to go to help. Monk eventually realizes he has no choice but to go get help. Thirty feet later, he begins to flag. After using most of his water to wash his hands, Monk continues no and finds metal debris. Hallucinating from the heat, Monk starts talking to himself. He collects the evidence and continues.
Natalie tends to Fletcher while Monk is forced to admit that he needs people and promises to be nice if he gets one more chance. He finally finds the UFO fanatics, who call the authorities. Later, Fletcher and Natalie meet with Monk at his hotel. They look at the evidence and Monk explains what happened. Kyle killed his sister for the money. However, nobody ever found his sister's body: the coyote's dragged it away. Monk saw Kyle's van at Marjorie's house and realized he worked at a model hobby store. Kyle used the models he had to make a fake UFO, attract attention, and count on the UFO fanatics to turn up the body.
Fletcher is relieved and goes to arrest Kyle while Monk goes to talk to his fans. He goes outside and tells them it was a simple murder, and that they should go home and stop wasting their time. Natalie is impressed at how empathic he is, but the crowd insists he's lying and Monk is covering things up. Monk gives in and tells them he's an alien. They're suitably impressed.
Later at home, Natalie informs Monk that Kyle confessed. Some of the UFO fanatics are still out there. As Monk cleans, Natalie tries to determine if he has a belly button. Monk refuses to show her and he's forced to take refuge in the bathroom.