Inspired by her late grandfather's entrepreneurial spirit, Natalie decides that Monk needs to go into business for himself as a private investigator. Monk is surprised to learn that Natalie has already taken the initiative and rented out an office, complete with décor straight out of a Hollywood detective movie. Monk tries to object, but with Natalie's enthusiasm and so much already in place, he can do nothing but wait in his new office for his first client.
It's a long wait, but eventually a woman walks in the door, a high-profile real estate agent named Linda Fusco. Someone has hit the fender of her car and left a note on her windshield that says "Go to hell," and she wants Monk to figure out who did it. With this being the only case to cross their paths for days, Monk and Natalie are left with no other choice but to take it.
Monk and Natalie head to the marina where Linda Fusco's car was hit. They talk to a possible witness, a small boat captain named Bill Gibbard, but he doesn't have any information. Back at Monk's office, Captain Stottlemeyer stops by looking for help in the case of a missing schoolteacher. Monk would love to work on the captain's case, but instead, he and Natalie must head to a restaurant to pursue a lead for Linda Fusco.
At the restaurant, Monk gets punched in the gut by an unfriendly manager, but they leave with the name of a possible suspect in the fender bender: Jay Bennett. Monk and Natalie track Bennett down, and though he denies any involvement, his behavior is suspicious. Bennett has a boat at the marina, so Monk and Natalie head there to check it out. Monk gets on the boat to look around, but while he does, Natalie makes a gruesome discovery: Bill Gibbard's dead body floating in the water nearby. She calls Captain Stottlemeyer, but meanwhile, Jay Bennett has boarded his boat and taken off onto the open water with Monk!
Captain Stottlemeyer arrives and puts everything together. He recognizes Jay Bennett's name from the missing schoolteacher case. Bennett must have killed the schoolteacher out on his boat, and when he came back to shore, he accidentally hit Linda Fusco's car. He wanted to cover his tracks, but he didn't want to attract any attention from potential witnesses to the fender bender. So Bennett pretended to leave a note with his name and address on Linda Fusco's car, but wrote "go to hell" on the note instead. The seemingly insignificant fender bender turned out to be crucial to breaking open a murder investigation.
The case is solved, but Monk is in danger. Bennett intends to kill him, and is chasing him around the boat with a flare gun. Monk can't swim, but he has no choice but to jump off the moving boat into the rolling water. Fortunately, Linda Fusco also has a boat, and she, along with Natalie, Stottlemeyer and Disher, make it out to sea in time to save Monk from drowning. Monk has helped solve both the fender bender and the murder, but he took a lot of physical abuse in the process. Solving crime as a hard-boiled "private eye" isn't Monk's style, and after this fiasco, and many apologies from Natalie, it's clear he'll be going back to his more cerebral type of detective work.