Jane and Maura investigate the mysterious death of a young boy whose family is from Cape Verde. It appears at first that he may have died during an attempted exorcism, and it may take a message from beyond the grave for Jane to pinpoint exactly what happened. Jane is distracted from the case when her mother sets her up on a surprise date.
The scene opens with a boy skateboarding. A black car pulls up and the boy gets in. At a clothing shop, Jane is trying on dresses. While in the dressing room, her mom says that all girls needs an LBD, to which Jane replies that she is vaccinated. She steps out of the dressing room in a gorgeous black dress, which her mom insists on buying. Jane gets a call and says she will be right there. Jane arrives on scene where they find the kid from the beginning of the episode. Maura is there too and she can’t find any stab marks or bullet holes. Jane sees that Lt. Grant is with the press and comments that that is all he likes about the police work and Maura tells her to keep her voice down. Lane continues talking about Grant not being a good cop. He walks over and attempts to get information. Jane snaps at him and tells him not to touch anything. Maura adds that they don’t want to contaminate the crime scene to cover for Jane's rudeness. He tells Jane to pick up a skateboard under the dumpster. Grant leaves and Maura sarcastically says that their chat went “well”.
The mother of the boy comes by to identify the body. She says that Matisse, the boy, changed after meeting the skateboarders and that the devil got inside of him. She doesn’t know the boys’ names and Jane assures her that they will do their best to find Matisse’s killer. Jane asks Barry if he knows anything about the culture of Matisse and his mother. Barry says that they are a secluded bunch of people who usually keep to themselves. Jane looks at Matisse’s grades and asks if Barry can run the gangs for "devils" and see if any skateboarders come up. She asks where Korsak is and Barry says he is at the coffee shop. Jane visits Korsak and he is working on his testimony for a case and she wants to know why he is working at the coffee shop. Korsak hints at the new employee of the coffee shop. Jane asks him to look up on the Matisse case that she has and Korsak obliges.
Jane goes to see Maura at the examination room and she doesn’t have a cause of death ye and that she is still working on it. Maura changes subject and says that she thinks Lt. Grant is attractive. Jane says that Grant was a suck-up even in Catholic School and used to call Jane fat. Maura fees bad about Jane being overweight in school and Jane asks what she was called. Maura says she was called boring. Back on subject Maura thinks that despite no sign of entry, a tox screen is still a good idea. She tells Jane that she found wax and burned feathers in his. All signs are pointing to an exorcism but she refuses to conclude an exorcism as cause of death. Barry shows a picture of the mom’s church and automatically knows that it is a front for other things. Father Reginald Cukoo runs the church and has been charged with everything from robbery to check fraud. While on parole, Reginald opened the church. Jane theorizes that the exorcism went bad and they dumped the body to hide it. However, she says that no one performs exorcisms these days and Maura says that the Catholic Church has been performing them for centuries and still does to “expel demons”.
Jane and Maura visit Reginald at his church with Matisse’s mother. Jane tells them they believe Matisse was killed by a botched exorcism. Maura speaks in Matisse’s mom’s native language and she tells Jane that she was showing condolences. Reginald admits that he did spiritual healing and says that the devil killed Matisse. He tells Jane that she can’t fight the devil and asks them to leave. Maura says that she was disrespectful but Jane says that Reginald is a phony and points out that he was wearing a poncho. Maura corrects her and calls it a “Boo-Boo” and that Christians in Africa have used them for years. Jane laughs at the word "Boo-Boo". Once again, Jane gets a call and says that she will be right there. She tells Maura that she has to go speak to Matisse’s father. Maura says that she will get Jane a “Boo-Boo”.
Jane visits Matisse’s father and he is devastated that his son was murdered. He says that Reginald the Father of the church is a crook and that he made his ex-wife give him all her money, including the child support. He tells Jane that they were going to get full custody of Matisse and that everything was in the works. Jane returns to the coffee shop and Korsak says that the mom was getting child support and tells Jane that he is working an undercover case. He wants to help the new employee out by staking out the coffee shop because someone keeps stealing money out of the till. So far $26 has been taken and Jane laughs and says that he needs to get to work. At the station Jane’s mom visits and Maura says that the Matisse’s death was not a natural death. Jane’s mom brought Jane’s dress that she bought and Maura compliments it. She also brought Jane lunch. Maura eyes it and Jane offers her one. Maura asks what the white substance is, making Jane sarcastically explain the "white and brown substances" (marshmallow and peanut butter) the way Maura usually talks about science. Barry says that Matisse was running with gang members and leader Jerome, has a record. Maura says that people get nicknames because they had to do something bad. They need to talk to Jerome.
At the skate park, Barry and Jane visit Jerome “Cruncher” and he says that Ali is a good kid. “Ali” is Matisse’s nickname. Jerome says that he is done talking to them. Barry says that he has not had a chance to get to the gym and Jane gives him the go ahead to grab Jerome. Barry grabs him and slams him on the hood of the car. Jerome says that he had nothing to do with the murder of Matisse and says that the church is evil that his mother goes to. Back at the station and Maura says that the tox screen is negative and Jane tells Maura to stop talking. She hears something and goes up to her car. She opens the door and there are snakes inside. Later Grant tells Jane to keep a low profile because someone is threatening her. He believes that Reginald is the one who did it, but it is political and he wants the charges to stick. He tells her to get Reginald but be quiet about it.
At a restaurant, Maura and Jane talk about how Matisse has no results that are positive from the tox report and Maura suggest that she can’t say for sure what it is. Hypothetically, she thinks that he was hexed to death because of the fear of being cursed. Jane laughs and says that Matisse wasn’t scared to death and Maura asks if she was afraid of anything. For Jane, she was scared of witches and Maura was afraid of a flesh eating disease. She feels like going to church. They go to the church and Reginald says that they are about to perform a ceremony and Jane says that she is about to serve a warrant. Inside Maura says that it is a bad way to get information with a warrant but Jane says that she doesn’t have a warrant and was only about to serve a warrant, which could be any time in the future, according to her. They watch the ceremony and Matisse’s mother feels that she has the devil that cursed Matisse. They do their ritual and a fire bomb is thrown throw the window. Barry kicks open the church door and finds a kid running away. Barry tackles him. It is Jerome from the skate park.
At the station they question Jerome who says that the Voodoo church that Matisse belonged to was evil and that he did not kill him. He says that he wants a lawyer and Jane puts him in lock-up. Jane walks out of the room and sees the dress that she bought and realizes that she is late for dinner. She tells Barry to call her mom and tell her that she is on her way. She arrives and her mother says that everything is fine. Jane goes out to the dining room and Lt. Grant is there. She walks back in the kitchen and her mother admits for setting her up and says that Grant is cute. She says that she doesn’t need to be setup like that. She re-enters the dining room and Grant says that she looks beautiful. They start to be attracted to each other and Jane says that it is a bad idea and walks out of the house with Wine. She visits Maura and wants to know if she looks pretty. Maura says that she is and is laughing because Jane doesn’t know. Maura feels that Jane doesn’t think Grant is a bad guy. She says that it is sweet that Grant is interested.
At her apartment, Jane is looking over the pictures and drinking beer on her couch and finds fresh blood on her carpet and floor when she accidentally drops a photo. She follows the blood trail and finds Matisse’s body. He wakes up holding a purple flower. Jane then wakes up on the couch to something breaking. She enters the kitchen and sees that a vase of purple flowers fell onto the kitchen floor, but there is no body. Later, Maura comes over in her pajamas and says that there are explanations such phenomenas. She suggests that the dog might have knocked it over, but Jane reminds her it was too high for the small dog to reach, and sarcastically wonders if ghosts might be real after all, if maybe she'll pick the winning lottery numbers today or if maybe she's losing her mind, to which Maura offers doing a brain scan. Jane says that she wants to have her run a tox scan on a poisonous purple flower. Maura tells Jane about the poisonous purple flower called monkshood, which is very hard to detect, but she says she will try anyways.
Later, Maura says that the tox report came up positive for monkshood and Jane asks if it is possible to trace the flower to the location. She says she cannot and Jane says that she has to lie about it, which Maura of course refuse to do.
They visit Matisse’s father and sees the same purple plant. Matisse’s father says that he never gave him flowers, and his wife keeps talking about "the crazy church". When explained how the killer used the poisonous flower, the wife says that "this is crazy", before Matisse's father turns to her and seem to realize she was involved. Jane suggests that the wife gave Matisse water that was tainted with the poisonous flower. She continues explaining that Matisse's father wouldn't have a baby with his wife, which she knew about since this commitment to Matisse was one of the major reasons he would get custody, and that the wife figured the church and Matisse's mom would be blamed because of the exorcism. The wife tells Matisse's father that his ex-wife would never give up custody and that she did it for them. Jane reads her the rights and arrests her.
Back at Jane’s, Grant is on the steps of her apartment. He says that he has to leave to go to D.C. and that he has a job as a liaison between the city of Boston and Homeland Security. He apologizes for teasing her in school and admits that he liked her for a really long time, which Jane seems to have a hard time believing. There is almost a kiss, but she says that she will miss him and then kisses him on the cheek before going in and leaving him on the steps.
- Angie Harmon as Detective Jane Rizzoli
- Sasha Alexander as Dr. Maura Isles
- Jordan Bridges as Officer Frankie Rizzoli, Jr.
- Lee Thompson Young as Detective Barry Frost
- Bruce McGill as Detective Vince Korsak
- Lorraine Bracco as Angela Rizzoli
- Donnie Wahlberg as Lt. Joey Grant
- Deidrie Henry as Beatrice Senna
- Michael Jace as Malcolm Senna
- Laura Leigh Hughes as Alicia Senna
- Charles Malik Whitfield as Reginald Perry
- Allen Maldonado as Cruncha
- Dabier Dubbydubbul as Mattise Senna
- Phyllis Lyons as the Waitress
- Gabriela Mankti as Tasha Cranston-TeLewis
Detective Jane Rizzoli: Yo, Dr. Death. J-Lo needs a cause of death, not a seminar on gangsta nicknames.
Detective Jane Rizzoli: [catches Korsak gawking] I'm guessing she's in the waitress protection program, and you're watching her because...
Detective Jane Rizzoli: [catching up]
What, are you going to tell me I filled out nicely?
Lt. Joey Grant: And risk charges? Maybe...
Lt. Joey Grant: I gotta leave for D.C. Soon. Just wanted to come by and see you before I left. Say bye, if that's okay.
Detective Jane Rizzoli: What's in D.C.?
Lt. Joey Grant: Big job I wasn't expecting.
Detective Jane Rizzoli: What, did they appoint you to the Supreme Court or something?
Lt. Joey Grant: [half-smiling] No, not that big.
Dr. Maura Isles: [Maura speaks in Creole to the mother of the victim]
Exorcisms are very powerful.
Detective Jane Rizzoli: Is that what she said?
Dr. Maura Isles: No.
Detective Jane Rizzoli: Is that what you said?
Dr. Maura Isles: No.
Detective Jane Rizzoli: Maura.
Detective Jane Rizzoli: Damnit! I am late for dinner! My mom is gonna kill me.
Detective Barry Frost: You were firebombed, Jane. It's a good excuse.
Detective Jane Rizzoli: You don't know my mother. Will you call her and tell her I'm on my way?
Detective Jane Rizzoli: How much you know about Cape Verdeans?
Detective Barry Frost: You mean, do I have any special insight because I'm black?
Detective Jane Rizzoli: [scoffing] Yeah. The gangbangers I've arrested are usually somewhat suspicious of white, female cops.
Dr. Maura Isles: Very intriguing culture.
Detective Jane Rizzoli: Descendants from the Portuguese explorers and slaves from the Cape Verdean Islands.
Dr. Maura Isles: I'm impressed!
Detective Jane Rizzoli: I can Google, too. And that Father Coku, or whatever, is a phony. Did you check out that poncho he was wearing?
Dr. Maura Isles: A grand boubou.
Detective Jane Rizzoli: I said I know.
Dr. Maura Isles: Oh you knew? What that robe was called?
Detective Jane Rizzoli: A boubou?
Dr. Maura Isles: Well it's popular with the Christians in West Africa. Though the Swahili and East Africans and Bantu speakers in Central Africa also...
Detective Jane Rizzoli: Like their boubous?
Dr. Maura Isles: [examining Jane's sandwich]
What is that white substance?
Detective Jane Rizzoli: Fluff.
Dr. Maura Isles: Light, downy particles of cotton?
Detective Jane Rizzoli: [pauses] It's marshmallow.
Detective Jane Rizzoli: And the brown substance is called peanut butter. It's ground up heavy, oily particles of peanuts. What, they didn't have that in your fancy boarding school?
Dr. Maura Isles: [eating] Oh, it's really good!
Angela Rizzoli: [upon seeing a dress Jane is trying on]
Oh! That's beautiful.
Detective Jane Rizzoli: [laughing] Yeah, if you're a farmer's wife. Ma, come on, my birthday was last month, it's fine.
Detective Jane Rizzoli: Well have fun in Washington.
Detective Jane Rizzoli: And I'll miss you.
- One of the many names of monkshood is "Devil's Helmet", a possible allusion to the episode title.