A cab driver in Los Angeles is intrigued by the scent of women. When a passenger enters his taxi and tells him where she is going, the driver tells her he is off duty. She pleads with him to take her and he acquiesces and they drive away.
Prentiss arrives home and removes a file folder and several passports from the safe in her bedroom. As she reviews the redacted document, her cat jumps on her lap and is wet. Frightened that someone might be inside she grabs her gun and searches her apartment and finds an open window. She calls her friend, who tell her that she left it open for the cat. Her phone rings and she sees "Unknown Caller" on the caller ID. She booby traps her windows and front door, pulls up a chair and waits silently in the dark with her gun in her lap.
"Hunting is not a sport. In a sport, both sides should know they are in the game." Comedian Paul Rodriguez
The next morning, the BAU discusses a case that involves three women who had been abducted and murdered in Los Angeles from different locations and socioeconomic strata. The women had been drowned, and their bodies were soaked in methanol and patches of skin had been incised from the bottoms of their feet. The team flies to California to meet with Detective Bailey, the primary on the case.
At the unsub's location, he appears to be performing an experiment and is seeking a certain smell.
The team determines the unsub drives a taxi based on the different locations of the victims. Although the victims were found nude, there are no signs of sexual assault. They think the fact that skin withers away independent of the body is what keeps him killing.
The unsub is bothered by certain smells and kicks a woman out of his cab because she reeks of food, cigarettes and perfume.
Detective Bailey doesn't know if there are more victims. The victims were soaked in methanol and the skin was removed post-mortem. They had chloroform in their blood and their nasal passages were irritated, so Hotch realizes the unsub had aerosolized it. Reid discovered that it's relatively easy to purchase methanol and graphs the geographic profile, which is large and the unsub is obviously mobile. They narrow it down to a police car or taxi. Morgan asks Garcia look into cab companies and she finds seven, but none had reported picking someone up in the area.
The unsub takes his next victim and smells her, unconscious. He listens to a recording about creating a natural scent by using animal skin.
Rossi suggests a gypsy cab, which would make him harder to find. Reid remembers using methanol in science experiments and clipping samples just like the skin. The unsub might be a scientist.
The unsub raises a body out of the vat of methanol as the terrified girl watches, now awake. He tells her she's going to live forever.
The BAU gives the profile to the police. They're looking for a very intelligent individual who won't be following the investigation. He's getting rid of any evidence by submerging the bodies in methanol. Someone will remember a confrontation with him. Just as they finish, they receive news of another body. Reid has Garcia look into a combination of purchases: beakers, tubing, methanol, chloroform, and other items for science experiments. The woman who the unsub kicked out contacts them and tells them he was listening to a recording of himself. She gives them the last two digits of his cab (33). The unsub is anti-social and delusional.
Morgan and Prentiss try to analyze the unsub's victim choices by sitting in a cab. He wonders if it's something the victim says and asks Prentiss what's bothering her. She doesn't respond and says it smells in the backseat. They realize smell could be the trigger. Reid says methanol can be used to make certain scents.
The unsub is using the victims to make candles and tells Anisa he's perfected the process.
Reid brings up an olfactory disorder called hyperosmia and says smell is a powerful trigger. Reid thinks he's trying to bring back a smell from his past. Garcia calls with an address.
The unsub is preparing to submerge Anisa. He tells her to take a deep breath and begins lowering her into the methanol as they arrive on scene. Rossi notices the camera and Morgan spots the cab speeding away. Prentiss and Reid search the house while the others take up the chase. They find Anisa and free her.
The unsub gets away when a truck pulls in the FBI's path and law enforcement splits up to search the city. Hotch and Rossi find him in an alley and speed after him. The unsub crashes under a truck, which peels away the top of the taxi. When they reach the cab, they hear his recording playing. He is dead.
Prentiss arrives home to find a box wrapped with a bow propped outside her door. She enters her apartment with her gun drawn. At the same time, Reid calls to invite her to see Solaris with him. She thinks Morgan put him up to it, but he just wants to go see the movie. She passes and says she's just going to hang out with her cat. She removes the file from her safe before going to open the box. Inside is a single lavender flower. She brings it to her nose and remembers the scent of the flower from the past. She is picking flowers in the garden below a large house when she is taken away by law enforcement. Ian Doyle is watching from the balcony and she asks to speak to Sean. Doyle makes a call on his phone and says, "they got her" as two agents arrest him. He tells the person on the phone to stay on top of this. A single flower has been dropped on the lawn.
"Nothing revives the past so completely as a smell that was once associated with it." Novelist Vladimir Nabokov
Prentiss tosses the flower in the trash can. She places the file in her go bag, calls picks up her cat, and leaves her apartment.