Natalie is out running errands for Monk when she can't believe her eyes: crossing right in front of her in a restaurant is a woman who appears to be Trudy Monk! Trudy is meeting with an older man named Zach Ellinghouse, and Natalie overhears her telling Zach that she faked her own death to protect her family from a dangerous extremist group that was the subject of a newspaper story she was writing. Now Trudy has come out of hiding to look for a key that belonged to her recently deceased ex-partner, Janice Ellinghouse, Zach's daughter.
Natalie tries to warn Monk about Trudy, but he's in such a good mood, she doesn't have the heart to tell him the disturbing news. Instead, Natalie follows Trudy to a clandestine meeting with Zach Ellinghouse. Trudy spots Natalie and confronts her, telling her that Adrian must not know that she's still alive.
Things take an even more alarming turn when Zach Ellinghouse turns up dead. Stottlemeyer and Disher are called in to investigate, and Monk goes along with them. At the crime scene, Monk finds some clues that lead him to a horrifying conclusion: the killer was Trudy! Worse, Monk actually spots Trudy lurking near the crime scene.
Monk goes into a tailspin. If Trudy is still alive, everything he thought was true is untrue. Desperate for answers, Monk goes to Trudy's grave. He realizes that the woman walking the streets of San Francisco can't be Trudy because, as he later explains to Natalie, visiting Trudy's grave "still hurt." With his mind clear, Monk sets his sites on finding the truth about this woman claiming to be Trudy.
Monk and Natalie talk to Trudy's old boss, a newspaper editor. He shows them an article Trudy wrote with Janice Ellinghouse, a story about corruption in the local dockworkers' union that relied heavily on an anonymous source. Looking at Janice's things, Monk deduces that she was renting a locker at a nearby storage facility. Perhaps what "Trudy" is looking for is locked up there.
Monk and Natalie head to the storage facility, where they wait for "Trudy" to show up. She does, along with Jack Bollinger, a big-time union official that Monk recognizes from Trudy and Janice's article. Bollinger took control of the union after the article put most of the union's leaders in jail. Monk realizes what's been going on. Bollinger must have been the anonymous source that helped put everybody away, and now he's afraid that his identity will become public after Janice's death. He hired an actress to impersonate Trudy and convince Janice's father to give up the key to the storage locker that held the incriminating notes from the article ... but something went wrong, and Zach Ellinghouse had to die!
Natalie calls Captain Stottlemeyer, but Monk can't wait. He's transfixed by the actress who looks so much like Trudy. Monk approaches as Bollinger and the actress search the storage locker. Bollinger shoots at Monk, but hits the actress! Stottlemeyer and Disher arrive just in time to arrest Bollinger, but they're too late to save the wounded actress, and Monk has to endure the pain of watching a woman who looks like Trudy die in his arms.
Quite an ordeal, but in the end, Monk is relieved to return to his old life, where Trudy may be gone, but her love remains.