The episode begins with Officer Hale driving his car and he sees an accident between two cares. He immediately radios to the dispatch. He then gets down checking the site. There is no one in the car but he sees blood dripping from the steering wheel of the overturned car. There is hair on it as well. He then announces his presence. We then see a woman strapped to the bed; she is wearing a nurse’s uniform. A man wearing a mask comes up to the bed with a knife and the woman screams. At home, Catherine and Steve are celebrating their Halloween by watching a scary movie. They then start making out but are interrupted when the door bell rings. It is Danny.
He is upset as Grace, his daughter, ditched him on Halloween by going over to her friends. He asks Steve for some beer. Steve goes in to get beer but comes out declaring that they need to leave; there is a case. Catherine offers to pick up Grace from her friend’s place. At the site, Ho tells Steve that this wasn’t an accident. The white Chevy was reported stolen earlier this day. It looks like the Chevy hit the red car multiple times, causing it to overturn. Ho then points out that the wires to the air bags were cut; looks like pre-meditate. The overturned car is registered to Lisa Heller, a 24 year old nursing student. They get a hit that Lisa’s credit card was used at a convenience store.
They pick up a suspect. He says that he saw the purse with some plastic in it lying on the ground. He tells them the location where he found the purse. They arrive at an alley. They check the alley and find Lisa’s purse. But Kono also finds Lisa’s body in a dumpster. At the morgue, Mac tells them that the “Y” marking on the body was made by the killer and also that the killer took the heart, kidneys and pancreas. The killer had kept Lisa alive when he removed her organs. Steve suggests organ trafficking as Lisa’s blood type is O negative. The next day, Catherine picks up Grace and she tells her that she needs to make use of the time she gets with her father.
Danny tells Steve that the lab results show that the hair from the steering wheel is goat hair. Max calls Steve and tells him that his internal examination shows that there was no effort made to preserve the organ. He asks Steve to come down to the lab. Max tells the duo that there is a ‘Pentagram’ symbol on the victim’s body; this could be a symbol of some cult. The knife had the symbol on it. This means this is a ritualistic murder. According to Lisa’s parents, she was supposed to go to the library but it looks like she didn’t. Kono goes through Lisa’s emails and finds out that she was supposed to go to a party and gets the details.
It is at a house that has been condemned 20 years ago and has been vacant ever since. Steve and Danny go to the house. Danny is spooked when Steve mentions that this place is haunted. Steve goes upstairs to check and Danny finds an injured boy in one of the rooms. His head is bleeding (it is make up) and he is awake. Danny calls Steve. The guy is Jesse Hills and he is shocked to learn that Lisa is murdered. He says that he threw a party here as he lives with his parents and wouldn’t have been able to do that at his place. He tells the duo that he was shooting a video for his facebook account and probably that could help. Kono and Ho go to a store and show the woman the picture of the symbol on Lisa’s body.
She says that they are looking at an athame which is a ritualistic knife used in ancient witchcraft. This did not come to her shop. She then notices a Hebrew letter in the symbol and she tells them that this is appears in the Mendes’ pentacle or the Satanic goat’s head. It is a popular image in black magic. At the same time, Steve and Danny go through the video. They see Lisa with Lucas, a guy Hills thinks he shouldn’t have called. They then see a man wearing a goat head behind the dancing couple; that is their guy! He followed Lucas and Lisa. It looks like they may have a second victim. And Steve is right. The killer is sharpening his knife and Lucas is kept in a cage.
The killer’s watch begins to beep and he wraps up his knife and goes up stairs and walks into the hall where we see an old woman watching television. The killer then sees that one of the old woman’s medications has run out and he goes to get it. She tells him to pick up some ice cream. At the HQ, Ho tells that there is no report of Lucas missing and also that the killer has a passion for the image of the Sabbatic Goat. This goat represents duality in nature; heaven and hell, man and woman. And that is why the killer took Lisa and Lucas. Kono then tells them about the roots of the Halloween festival in some traditions where the first sacrifice is made on the Halloween midnight and the second one is made on the following midnight.
There is a chance Lucas is alive and they don’t have much time. They then look into cruelty cases with animals on Halloween night sin the past decade, as they haven’t found any murders that match the present MO. And there is a match found; Seth Tilton. He has no priors but he has a juvi record. His grandmother took custody of Seth and he still lives with his grandmother. At the house, Lucas manages to free himself from the cage and walks into the hall and asks Helen about Seth. Lucas realizes that Helen is his tormentor’s grandmother. He goes to the phone to call the police. He calls 911 and Helen stabs him from behind. Kono informs Steve and Danny about the 911 call. Seth arrives home and finds Lucas’ body on the floor.
Helen looks at him sternly and he says he is sorry. She tells him that she is tired cleaning up his mess. Seth then drags Lucas’ body and Lucas is conscious. The cops arrive and Danny follows the blood trail but he doesn’t find either of them. Steve places Helen under arrest. She is being driven to the station and she fakes a cardiac event and shoots the officer who is driving her to the station. She then calls Seth and tells him never to return home. She tells him to take care of himself. Danny and Steve realize that they got played, and arrive at the scene where they see that the officer is down and Helen still has the gun with her. Steve announces himself and Helen shoots herself.
Steve takes her phone and sees the last call made. They manage to get Seth’s location and they realize that he is going to complete the sacrifice. Seth is about to stab Lucas when Steve and Danny arrive and they shoot at Seth. Lucas is saved. At home, Catherine and Steve are watching the scary movie and making out; but since Steve hasn’t seen the ending of the film, he is distracted. Danny and Grace arrive in their Halloween costume. Catherine suggests that everybody should watch ‘The Notebook’. Grace is excited. And the four of them sit down to watch the movie. The episode ends.