A man is coaching Little League baseball and his son Petey is at the bat. Petey hits the ball and it goes over the fence as everyone applauds. Another boy goes around the fence to get the ball and finds an old female jogger, Martha Murphy, lying on the ground, killed by the baseball.
Later, the woman's daughter and her wife go to clean up things at her house. As they go through her belongings, they find a package with a Nobb Hill mailing address with a voodoo doll in it. A miniature baseball has been glued to its head and its postmarked three days before Martha's death.
At the station, Disher and Stottlemeyer are studying the voodoo doll when Monk and Natalie arrive. Monk is distracted by the fact they've rearranged the office. They finally put everything back the way it was and he can concentrate on the case. Stottlemeyer explains about the postmark and Monk makes a startling discovery: one of the garbage cans wasn't put back where it was supposed to be.
Monk and Natalie go to the baseball field with the police, but the detective has no explanation. Natalie admits that she used to laugh about voodoo but now she believes. Disher suggests that the killer knew she came by every day and used a pitching machine to kill Martha. Natalie points out that there would be a second baseball if that were the case. She continues to dissect their theories and insists it's voodoo, but Monk insists there is always a rational explanation. Natalie refuses to explain why she believes in voodoo.
The gang is called to the apartment of Ralph Ferris, who died during a lightning strike when he was playing golf. The land lord discovered Ferris received a package postmarked a week earlier. They open it and discover it contains a doll with a lightning bolt stuck in its head.
Later, Monk is vacuuming at his apartment and surprised when Natalie arrives early and says they're going to a resort in Santa Barbara for a vacation. She's eager to go but when Monk says he has to let Stottlemeyer call, she agrees to do so. However, Monk points out that he unplugged the telephone cord to vacuum. He asks what her problem is and she reveals that Stottlemeyer called to tell her there was a third voodoo death.
Stottlemeyer and Disher meet with dead man Robert Boyd's niece, Angeline Doerth. Outside, Natalie drives Monk to the building but refuses to go in. Angeline explains that she heard her uncle scream after the mail arrived. She came down and tried to resuscitate him but it was too late. Angeline had moved back to help her uncle because she was the only family he had. Monk finally comes in and explains Natalie's reaction. Stottlemeyer explains that according to Angeline, her uncle was obsessed with the voodoo deaths. Monk examines the crime scene and notices an upside-down horseshoe over a door. He notes that the horseshoe is hanging down when traditionally they're supposed to point upward for good luck. He introduces himself to Angelina but before he can question her, Natalie calls Stottlemeyer, who says Monk needs to take care of her. Monk practices being warm and caring by offering his condolences to Angeline.
Stottlemeyer and Disher go to the occult store that sold the dummies. The owner is busy selling more dolls and the officers go over to talk to Reverend Jorgensen, the owner. Jorgensen denies any involvement with the killings and insists his advertising and sales are legal.
Monk goes to see Natalie and explains that he can't function without her. She can't bring herself to speak, but points to the kitchen table where there's a package containing a voodoo doll with its head cut off. Monk calls the police and examines the package for clues. He notices that her name is misspelled "Teager." She worries about what will happen to Julie and Monk insists that someone is trying to scare her and there's no such thing as voodoo. Natalie finally admits that when Mitch began her tour, they lived in South Carolina in an apartment next to a voodoo priestess. She told Natalie that Mitch was in danger and the next day he was shot down. Stottlemeyer and Disher arrive and Monk shows them the doll.
That night, Natalie is trying to sleep and eventually leaves her bedroom when she notices the overhead fan spinning above.
The next day, Disher stands watch while Monk goes to the station with Stottlemeyer. He tries to reassure Natalie and says they'll put her in a safe house later that afternoon, and insists there's no such thing as witchcraft. Natalie isn't convinced.
The mayor goes public with the deaths and copycats are flooding the city with dolls. Monk notices that each package has a label but otherwise doesn't have a clue. He tells Stottlemeyer that Natalie is losing it and it will take forever for him to get a new assistant. Stottlemeyer comes up with an idea to reassure Natalie. They call in Jorgenson to Natalie's house to perform a cleansing ritual. Monk soon starts to object at all the dirty evil-smelling rituals, but Jorgensen asks him to reattach the doll's head while he continues with the ritual. It takes him a while. Finally an impatient Natalie drinks his potion, only for Jorgenson to reveal she was supposed to apply it to her neck.
They call an ambulance and Monk realizes that Angeline is one of the paramedics. The paramedics take Natalie away and Angeline insists there's not enough for Monk to ride along. Jorgenson offers him a ride to the hospital and realizes that Angeline was the attending paramedic at all the deaths. Jorgenson admits that Angeline is a customer and Monk realizes that Angeline is the connection. Her uncle was loaded and she killed him, and then used the other dolls as a distraction. She initially mailed the boxes to herself to get the proper postmarks, and then stole Martha and Ralph's keys to hide the boxes in the dead person's houses. She then used an untraceable drug to trigger a heart attack in her uncle and planted good luck charms around the house to make him appear superstitious.
In the ambulance, Natalie wakes up and notices that Angeline has misspelled her name "Teager." She struggles with Angeline and the paramedic gets the upper hand. Monk tells Jorgenson to ram the ambulance, knocking it off the road. Monk gets Natalie out while Jorgenson decurses the ambulance.
Later, Monk explains that Angeline was trying to distract him when she thought he was getting too close. Monk refuses to admit that he was distracted by Natalie being threatened. She admits she's happy to have been proven wrong and Monk welcomes her back to the world of rational thought… while stopping to touch parking meters.