Monk decides to purchase a beeper, although Natalie is less then thrilled when she finds out he wants her to pay for it, and it's for her. She then notices a couple watching Monk, a couple whose daughter Amanda Clark died. Plague by guilt, he ends up agreeing to take the case before they can even ask.
Monk takes Stottlemeyer and Natalie to the park where the daughter was killed and talks to the witness, Tom Donovan. Despite some interruptions from Randy, Donovan tells of how he saw several men stab her and carve a sun symbol in her chest. Before she died, she talked about "Father" and they've determined that she was a former member of the Siblings of the Sun cult, before becoming a prostitute a year earlier. Monk volunteers to infiltrate the cult but when Stottlemeyer points out it's a bad idea, Natalie decides to volunteer. They approach two cult members in the street but when they're only interested in people with no family, they catch on that Natalie has a daughter. Monk takes over and they offer to take him to their ranch and put order in his life. They call in a van and take him away.
While the two people, Brother Ted and Sister Sally, show Monk around the ranch, they spot Father and Monk asks why he isn't upset. They quickly cover and Monk then talks to another person, Brother Zack, who was an eyewitness alibi to Father during Amanda's murder. Zack says that he only heard Father talking to God and heard a microwave oven beeping. Monk wonders if Father snuck away but quickly tries to pretend he's unconcerned. He then looks around the place and finds scratch marks in the dirt behind Father's cabin, but Father finds him and chats with him, offering answers when he finds Monk has lost his wife.
Randy tries to interrogate Brother Ted, without much luck, while Natalie tells Stottlemeyer that Monk is in the cult. Father holds a rally and while claiming he's never been sick a day in his life, tries to get through to Monk, forcing him to confront his fear of charcoal. He gets Monk to give up his wipes… eventually.
Later, Stottlemeyer checks in to report he found Monk at the airport, selling flowers. Monk is busy organizing flower bouquets at the ranch when Father asks to see him. Since Father is reluctant to bend over and plug in his hot plate, Monk helps and spots something like a pen cap. Father then asks Monk if the police sent him, and admits he wasn't happy when Amanda left but he didn't kill her. Monk insists on staying so he doesn't have to think, and Father agrees to let him stay. He asks Monk to turn over all of his money, but they're interrupted when Stottlemeyer, Natalie, and Randy arrive to take him away.
They get him in an apartment and with Kroeger's help try to unbrainwash him, but even Natalie is impressed when he reveals he doesn't need a wipe. Stottlemeyer tires to get through to Monk showing him photos of Amanda's corpse but has no luck. Randy then goes in but ends up signing along. Kroger goes in and tries to get through to him, but Monk even ignores the fact Hank Crenshaw supposedly resisted the cult. Kroeger reveals that Father has $20 million but it's not until the doctor crumples up the photos of Trudy that Monk snaps out of it. When Kroeger's beeper goes off, Monk realizes what the beeping noise that Brother Zack heard.
Monk and the others go to see Tom Donovan and Monk accuses him of hiding something. Donovan's wife Susan comes in and Monk confirms that Father was at his cabin, and the beeper was for a doctor. The cap was from a syringe and since Father claims never to be sick, Father put in a secret door so his doctor could give him regular injections of cortisone. Since Donovan swore that Father was at the murder scene. Susan shows them a photo of Donovan taking Amanda to the hospital, taken when he ran a red light. They go to see the car and Monk explains that Donovan was with Amanda as a client when he had his picture taken. He killed Amanda to cover up his affair and framed Father. Monk points out that Amanda is wearing a seatbelt in the photo, but there's no blood on the seatbelt from her ten stab wounds.
Later, Natalie is carrying groceries for Monk when Father comes to thank him for clearing his name. He asks Monk to come back to the ranch and Monk refuses, but does ask him to tie his shoe. Since Father can't due to his ailments, his followers are forced to question how immortal he actually is.