An elderly woman is walking near a little league baseball field when a foul ball hits her in the head, killing her. Days later, the deceased woman's grandchildren find a package in her apartment. Postmarked days before her death, the package contains a voodoo doll dressed to look like the dead grandmother, with a tiny baseball glued to the side of the doll's head.
Monk is called in to investigate. With nobody able to explain how the voodoo doll seemingly predicted the woman's death, Natalie argues that the doll must have possessed real magical powers. Monk scoffs, but the mystery grows when the police find another voodoo doll at the home of a dead golfer who was struck and killed by lightning. As with the first incident, the doll arrived in a package postmarked before the deceased's death, but this doll featured a lightning bolt glued to it.
The pair of apparent voodoo killings has Natalie spooked. When Monk is called to investigate the discovery of a third voodoo doll, Natalie refuses to enter the location. This time, a young woman named Angeline has found her uncle dead of a heart attack moments after he opened a package containing a voodoo doll with a broken heart attached to it.
But if things weren't scary enough for Natalie, she's soon horrified to receive a beheaded voodoo doll with her name on it. Monk tries to reassure her that there must be some logical explanation for what's going on, but Natalie isn't hearing it. She explains that years ago a voodoo priestess predicted her husband's death, and she's believed in voodoo ever since. Unfortunately, there are no leads in the case. The voodoo storeowner who's sold all the dolls has alibis for all three deaths, and there's no apparent connection between the three "victims."
Fearing for her life, Natalie agrees to let the voodoo shop owner perform a ritual to cleanse her of evil spirits. When Natalie mistakenly drinks one of the storeowner's toxic potions, she's rushed to the hospital in an ambulance. Monk is surprised to see that Natalie's paramedic is Angeline, the niece of the heart attack victim. While Monk and the storeowner follow the ambulance in the storeowner's van, Monk makes a realization: Angeline was present as a paramedic at all of the "voodoo" deaths. And the voodoo shop owner knows her too-she bought voodoo dolls from him!
Monk puts it all together. Angeline decided to kill her uncle and make it appear to be part of a string of bizarre, voodoo killings. Being a paramedic, Angeline was first on the scene at the first two deaths. She got the victims' addresses from their wallets, and then planted the seemingly prophetic voodoo dolls in falsely postmarked packages at the victims' homes. To kill her uncle, she gave him drugs to replicate a heart attack, and then simply planted a voodoo doll to make the death appear to be part of the larger pattern of killings.
Meanwhile, in the ambulance, Natalie also realizes that Angeline is a killer. Natalie tries to escape, fighting for her life with the murderous paramedic. Monk and the voodoo shop owner push the ambulance off the road with the shop onwer's van. Natalie, who has won her fight with Angeline, emerges victoriously from the ambulance, and then collapses from the ordeal.
Later, Monk tells Natalie that Angeline sent her a doll to distract him from solving the case. Natalie is relieved that her superstitions turned out to be nothing, and Monk teases her for being irrational. Of course, Monk can be plenty irrational, as he demonstrates by touching every parking meter he walks past.