Ever since a 1962 unsolved train robbery made it famous, people have made their way to the little town of Trouble in California's gold country. Some people come to see the Gold Rush Museum. But most come searching for the booty that the train robbers supposedly dumped off the Golden Rail Express in the botched heist. When the museum watchman a retired SFPD cop, is murdered, Monk and his assistant Natalie are sent to investigate.