Natalie and Monk are driving through the Nevada desert on their way back from a wedding when their car breaks down. While Natalie tries to fix the car, Monk wanders off to find cell phone reception and spot... a UFO!
After a night in a local hotel, they take the car to the nearest auto shop, where Monk proceeds to disrespect the shop's owner, eliminating any chance of the car being repaired in a timely way. Thanks to Monk's poor interpersonal skills, he and Natalie find themselves stranded in the tiny desert town of Vintonville.
They go to the local sheriff's office to report Monk's UFO sighting. While there, a local resident is reporting the disappearance of her neighbor, a woman named Marge Larkin. The town's top lawman, Sheriff Fletcher, doesn't take the report seriously, as Marge has been known to take unannounced vacations in the past. He's more interested in Monk's UFO sighting.
That night at the hotel, the flying saucer reappears once again, this time in front of Monk, Natalie, and a hotel clerk who films it on his phone. Natalie, who has been skeptical, finally believes Monk.
The next morning, Monk wakes up to find an alien staring at him through his hotel room window! It turns out that the hotel clerk posted footage of the UFO online, and Vintonville is now host to a bevy of avid UFO enthusiasts, including some in alien costumes. The UFO fans become obsessed with Monk when they discover he made "first contact." When the enthusiasts find the UFO "landing site," Monk tags along and tries to conduct a rational investigation. His hand gestures and quirks lead the enthusiasts to believe that Monk is actually an alien.
Then, some of the UFO enthusiasts find Marge Larkin's body out in the desert, and Sheriff Fletcher asks Monk to help with the investigation. Monk agrees and goes to see the body in the morgue. The initial theory is that Marge fell while hiking, but Monk realizes that Marge's hiking clothes are brand new, so someone re-dressed her after death. This is a homicide.
Monk goes to Marge's house to investigate. He meets Marge's only remaining next of kin, her brother, Kyle. After looking around, Monk concludes that Marge was killed and dressed in her home before being moved to the desert.
Monk goes with Natalie and Sheriff Fletcher to the site in the desert where Marge's body was found. There, he realizes that coyotes dragged Marge's body several miles from its original location. Suddenly, someone shoots at them from above, hitting Sheriff Fletcher in the leg. The sniper shoots out the tires in the Sheriff's jeep, and drives away, leaving Monk, Natalie, and the Sheriff to die in the harsh environment. Natalie stays with the sheriff and sends Monk to find help. Monk finds an abandoned campsite where someone built a model aircraft along with the same eyeglass wipes he saw Marge's brother Kyle use earlier. He collects the evidence and continues to trudge his way through the desert. Finally, the UFO enthusiasts find him. Monk, exhausted and chagrinned at being found by the annoying UFO enthusiasts, collapses.
Monk wakes up in the hospital. He tells Sheriff Fletcher and Natalie that the UFO sightings and the murder are connected. Marge's brother Kyle is responsible for both. He wanted to inherit his sister's money, so he killed her, dressed her in hiking clothes, and left her body to be found on the side of a desert road, dead from an apparent hiking accident. Kyle waited eagerly for her body to be discovered, but his plan went awry when coyotes dragged her body from the road and into the vast desert. Without a body, Marge couldn't be declared dead, and Kyle couldn't collect his money. It would be too suspicious for Kyle to find the body himself, so he built the UFO out of a model plane kit (he used to own a hobby shop), knowing that a UFO sighting would leave the desert crawling with people who would eventually find Marge's body.
Monk has solved the case of Marge Larkin's murder, but he has a more difficult task remaining. He must convince the UFO enthusiasts that the UFO was a hoax, and that he is not an extra terrestrial. Unfortunately, the only way Monk can get the enthusiasts off his back is to admit to being an alien. What the enthusiasts don't understand is that while Monk's behavior is often bizarre, the only otherworldly thing about him is his ability as a detective.