In Manhattan, New York City, Fashion Week is taking place. Model Hailey Vaughn arrives and the photographers are excited trying to get her picture as she's posing for them. Suddenly, one of them starts walking to her and her agent stops him. The photographer goes crazy and he hits the man with his camera. They both struggle on the floor to the horror of Hailey until the agent, who's been hit in the head takes a pen from the photographer's shirt and sticks it in his neck. Both men die.
In another event, models are walking on the runway. The place is crowded. A security guard is watching when he suddenly jumps onto the runway and grabs one of the models. The girl is screaming. Both are struggling but the man breaks her back and kills her instantly.
Felix welcomes Hood and Rachel and he's filling them in with the recent events. He says the air has been tested for toxins but the results came back negative. Hood asks if there's any connection between the murders. He says no. Hood asks to see the model. Rachel says she's Hailey Vaughn. Felix tells him she's the famous model. Hood is clueless. Felix leaves. Rachel asks Hood that if it's not airborne then what it is. Hood thinks it's probably cocaine. Rachel says there's nothing glamorous about it. Hood doesn't believe that people live for that stuff and want to die for it.
Hood, Rachel and Felix are looking for possible leads. They haven't found anything out of the ordinary. Hood wants to start with the living.
Felix is interrogating the bodyguard. He tells them that he seems to be a nice man since there's nothing wrong or bad with his records. The man can't explain what happened. In another room, Rachel is doing the same with Hailey Vaughn. She asks the model if she was seeing any of those guys. She says she's never seen the photographer before and that her agent is very professional. Back to Felix, he's trying to make the man talk by telling him that he used to work at a strip club and how even when you're professional, you can snap. The man says that's how he felt, but that everything is a blur. He says that he and that model had a connection. Felix asks if he's on any medication. Heidi tells Rachel she only had champagne on the way to the event. The bodyguard says he didn't eat or drink anything, he wishes he had that excuse. He didn't want to hurt the girl.
At the model agency, the receptionist, Gretchen, is on the phone talking about a previous date she had. Hood and Rachel show up. They want to talk to the agent's partner. The partner was also his wife, her name is Coco Delgado. They had been working together for 8 years. Rachel asks if they had a happy marriage. She says the first couple of years were happy, but then with the success of the agency it wasn't the same. She thinks her husband got into the fight over Hailey because he was very protective of his clients. Hood asks Mrs. Delgado if her husband was using something out of the ordinary like a different soap. She says no, but she hadn't seen him that much lately because of the Fashion Week.
Hood and Rachel leave and he thinks the woman is hiding information. Rachel wants to talk to the receptionist, who's also Mrs. Delgado's assistant.
Hailey opens the door to her apartment. It's the doorman and he's brought her mail. She says she usually gets it herself, but the man says that he couldn't help smell her perfume when she came in. He tells her she smells very good. She tries to close the door but the man breaks in.
Hood and Rachel are talking to Gretchen. It looks like there's something she won't tell. Rachel asks her to tell them what she's been dying to say. She says that the agent had been seeing someone lately. A client. It was Hailey Vaughn.
Hood and Rachel arrive at Hailey's apartment. Rachel notices that her door is open: no one is NYC leaves their door open. The apartment is all trashed. Hailey is found dead on a chair, neck snapped. Both hear a noise. It's coming from a window. The doorman is sitting on the outside, his hands covered in blood. He's crying. He says she was so beautiful and he doesn't know why he did it. Suddenly the man lets himself fall. Hood and Rachel are shocked.
The forensic team arrives at the apartment and is taking evidence. Hood is looking at Hailey's body. He notices three brown marks in her arms and neck. Felix tells Rachel they didn't find anything unusual and gives her some of Hailey's personal items. Among them, there's a promotional box of perfume and has the name of the manufacturer. Hood asks if she wears perfume. Rachel says yes. He asks her where she puts in on. She shows her both her wrists and her neck. They match the marks on Hailey's body.
Back at the agency, Gretchen gets Mrs. Delgado's mail. Then she gets a phone call from the guy she dated and he asks her out again that night. She's very excited about it.
Hood and Rachel visit the manufacturer's office. They talk to a man, Mr. Merced, who's telling them the story about perfume and its origins. He introduces them to Renny Boyle, one of the chemists. He tells them that most fragrances are also used to flavor foods, 60%. Less than 10% is perfume. Hood says how some perfumes don't have many ingredients, so you can put whatever you want there. He says how a perfume contained high levels of estrogen and had to be taken out of the market because it was causing cancer. Mr. Merced says that doesn't happen with his perfumes. They use the purest of ingredients. Rachel shows him the box of perfume found in Hailey's apartment. He says that the perfume, Fervor, was sent to 100 people, including fashion industry people. He says Hailey got one of those. Rachel tells him she's dead. They all go to talk to his attorney.
The attorney says there's nothing dangerous with the perfume. Hood tells her probably not to the person who wears it but to the person who smells it. Rachel wants the list of the 100 people who got the perfume. The attorney refuses saying that she doesn't want to cause panic. Rachel will get a warrant. Mr. Merced says it's probably a misunderstanding because no ingredients are put in the perfume without his authorization. Hood wants to run some tests to the perfume. Rachel also tells them that if they find something dangerous on the tests, the company will be their primary suspect. Hood and Rachel leave. The attorney tells Mr. Merced that if there's anything wrong with that, he will take the fall and he will take it alone.
Felix meet Hood who's analyzing something. He asks Felix to write something on a blackboard, some ingredients. One of those is civet musk. They use the musk in perfumes to make the smell last longer.
Felix says that they also use beaver glands in some perfumes. Hood says not anymore because it was an endangered species and because there was a fear that if the animal had a disease it could be transmitted to humans. Felix concludes that if the diseased oil is in the perfume it could cause people to go nuts. Hood is thinking about it and he will run some more tests.
Merced calls Boyle to his office. He asks him if he has any idea why the FBI was there asking questions. He thinks is because they believe the perfume is driving people crazy. Merced asks him if all the proper tests have been run. Boyle tells him he did exactly what he asked for. He always has. And there's nothing to worry about. After Boyle leaves, Merced takes a bottle of the perfume with him.
Merced is at a hotel room. A prostitute comes in and sits on the bed. He wants her to wear the perfume. She does so. Merced is sitting at a chair and watching her.
Rachel joins Hood and Felix and has the autopsy reports. She says that the same marks were found on the runway model, so it has to be the perfume. Hood and Felix are studying the ingredients written on the blackboard. Rachel asks Hood what he's thinking. Hood thinks they're using pheromones. Hood says pheromones have gene typing just like blood typing which is why certain pheromones attract certain people. And has to do with chemistry between people, Rachel says. Hood says that's why only certain people were becoming violent. But Hood thinks he's using something else. But he doesn't know what yet.
Back at the hotel room, the prostitute says she has another appointment and she has to leave. Merced was writing some notes and asks the woman to be quiet. She's about to leave when he stops her. She's not going anywhere.
Rachel, Hood and Felix get to the hotel room. Merced is dead. The girl shot him. Hood talks to her. He asks her if he made her wear perfume. She's very upset, she says she didn't know what else to do. Hood understands. He tells her he was conducting an experiment and it went out of hand.
Hood is analyzing something he found in the hotel room. It's a neurotransmitter molecule. It's like a messenger for the brain, telling us what to think or feel. Hood says they only know what half of them do. Hood says what he knows is that the one he found makes people go crazy. Felix asks how come that wasn't found in the sample they got from the manufacturer. Rachel says because the sample Mr. Merced created was clean. She also says that by his notes he was worried about someone altering his creation after they talked to him and decided to test the perfume himself. So he's innocent.
Hood, Rachel and Felix pay a visit to the attorney. They did a research on the perfume's patent. Apparently, Boyle claims to have invented it too. Hood wants to talk to him, he needs the formula so they can contain it. He's not there; he called in sick in the morning. There are no files left in his computer, they were erased. Hood has a thought. The marks of the perfume might have the answer.
Hood asks Rachel how can you affect a color or a pigmentation change in the skin. The simplest way is to go directly through the brain and tell the neurons in the body to tell the skin to get darker. Rachel wonders if it could be a side effect for a tan lotion that was being developed. In one of the files Rachel finds that it was some kind of love potion. What Hood thinks is that Boyle discovered that by accident and then mixed it with pheromones to lower the inhibition and increase the sex drive. But then it lead to violent urges. Hood also thinks that could've been marketed as the world's first scientifically proven aphrodisiac if it hadn't been for the side effects. Rachel wants to get all the bottles back.
Gretchen is getting ready for her big date and wears the perfume.
Felix is on the phone with Hood (who's at the agency) and has recovered most of the bottles that were sent out. Hood asks him to get some kind of inhibitor from a NY organization that blocks the receptors of the perfume, just in case. It's some kind of antidote. Rachel and Coco Delgado meet Hood and she's grateful that they had come and she thinks she saw her assistant with the box of perfume. But it is gone. Rachel calls her but she gets no answer. Gretchen doesn't answer because she doesn't recognize the number. She's in a taxi on her way to her big date. The driver asks her about it. She's feeling uncomfortable. Then the driver takes another route. He says it's a shortcut. Gretchen asks him to pull over but he won't listen. He's clearly affected by the perfume. He says he loves it.
Felix is with the attorney and they're watching the surveillance tapes to see if there's indication of Boyle's whereabouts. They see him taking an invitation. To a fashion show.
Hood and Rachel are on the street and she gets a call from Felix. He tells her what he found out and he's on his way to the event. Both Rachel and Hood are on their way to find Gretchen with the help of the police.
Boyle is at the fashion show and carries a bottle of perfume with him.
Gretchen is struggling with the taxi driver. She kicks him, leaves the car and runs away. Rachel and Hood have located the taxi, through a GPS.
Boyle is in the dressing rooms and tells a model that the designer wants her to wear the perfume.
Hood and Rachel have found the taxi but neither the driver nor Gretchen are there. Hood spots the bottle of perfume. Rachel calls for a canine unit, so they can track the scent.
Gretchen keeps running but stops at a gate. There's no way to go on. The driver gets to her. He says he won't hurt her because she smells so good. The police and the dogs find Gretchen and take the driver. Rachel comforts the girl. Hood gets a call from Felix. He hasn't found Boyle, but he thinks the models are wearing the perfume because men seem to be going crazy.
Hood arrives at the fashion show. Felix finds Boyle and arrests him. He says he had been working on that perfume for nine years. He created it and it should be his. He wants to see Hood stop it. Hood asks a coordinator the source for the smoke jets. Both he and Felix find them and pour a bottle of the inhibitor in them. The antidote is spread on the audience with the smoke. It works.
The event is over and Felix says how he might give up on the cologne for a while. He says that Rachel is some 20 blocks away, they could take a taxi or the subway. Hood prefers to walk. They could use the fresh air.
Rachel and Gretchen are on the street. Gretchen is trying to get a hold of her date but he doesn't answer. She's stood him up a couple of times. Rachel asks her to give her the phone. Rachel dials and leave a voice message, saying the she helped the FBI solve a case tonight. Gretchen says that she's starting to believe that there is no such thing as chemistry. Rachel tells her that she knows, for a fact, that it exists. Gretchen thanks her. She gets in the police car and is taken home.