A man, Bob Dunn, is getting dressed while listening to a newscast about a gruesome mutilation murder. He goes out for the night but his girlfriend who is on an out-of-town trip calls and wonders where he was and why he didn't answer his phone the previous night. He promises he'll see her the next night. He then goes to a bar to pick up women. He approaches a blonde and says she's his kind of girl, but her boyfriend arrives. Bob spots a brunette and uses the same pickup line. They end up back at his place and as they start to kiss, she breaks his neck. Later, Bob's girlfriend waits for him to call. When he doesn't she tries to call him, unaware that the brunette is in the bathroom examining her face, in particular her bright blue eyes. On the bed, Bob lies with his spinal column severed.
Olivia is at home talking with Rachel's friends, Neil and Helen, who have brought their son Graham over to play with Ella. The couple talks about how they met via a matchmaking service that lets them live separately but be together occasionally. Rachel gets a letter from her husband Greg, telling her he's filing for divorce. Charlie calls Olivia and the Bishops in to check on Bob. Meanwhile, Walter determines that Bob was essentially deveined. Peter asks how Olivia is doing but she says it's just home stuff. Walter concludes that someone bit open Bob's spine.
Olivia reports to Broyles, but notes that Walter has determined the teeth marks are human. Bob's car is missing and they're running a search. After the briefing, she asks Broyles about his divorce attorney and he gives her the man's number.
Astrid gives Walter the lab work on the victims and he points out someone took the victims' spinal fluid. There are traces of syphilis bacteria on the victims' spinal column, a form that has been extinct for decades. Olivia contacts the CDC, who confirm the syphilis bacteria was shipped to Lubov Pharmaceutical four weeks ago. They've reviewed Lubov's requests for the last year and determined Lubov asked for a number of contagious disease samples. They take the information to Broyles. Lubov also procured a substance useful for making biochemical weapons, and was used in the rapid skin-growth toxin the ZFT created.
They trace the delivery and Olivia leads a team to the address. They find a man in a wheelchair cutting open a dog and arrest him. They confirm he's Dr. Nicholas Boone, head of Lubov Pharmaceutical, a one-man operation. They show him photos of the victims and ask about his connection to ZFT. He finally admits that someone was dosed, but refuses to answer their questions unless they help him get his wife Valerie back from the ZFT.
Boone explains that ZFT is using his wife to blackmail him into conducting his experiments. Olivia confirms that she's missing and insists on trying to help Boone so they can get a handle on ZFT. Boone gives them an address that leads to a Chinatown restaurant with high power usages. Broyles authorizes Olivia to investigate.
Walter and Peter go to Boone's laboratory and wonder what he was doing. Meanwhile, Olivia is heading for the restaurant when Rachel calls to inform her that her husband is seeking sole custody of Ella. Rachel vows she'll run and disappear with Ella, and Olivia tries to reassure her before signing off. They go into the restaurant and enter the basement, arresting everyone there. There's no sign of Valerie. When Broyles tells Boone they didn't find his wife, Boone says he knew and asks to talk to Olivia. He tells her to go to a room in the back and there's something in it he needs. Inside are five vials of contagion, and he needs them to create an antidote. He explains that they infected his wife as punishment for his trying to leave ZFT and she's the one committing the murders.
Walter examines the spinal column of the dog while Peter finds a video recorder with footage of Valerie and Nicholas.
At a bar, Valerie approaches a man and picks him up. They drive to a quiet street and start kissing, but he notices she's running a temperature. She apologizes, grows fangs, and rips into his neck.
The police discover the corpse and Charlie runs a check. Broyles shows Olivia the video that Peter found, and points out the date. They go to see Boone and show him the footage, which shows him walking three weeks ago. Boone explains Valerie needs to feed to survive, and he gave her his own spinal fluid until he couldn't keep up with her hunger. The contagion burns through her spinal fluid, and Valerie kills to "refuel." He obtained the samples to try and find a cure, but ZFT wants it as a carrier to alter Valerie and others, for the purpose of showing off to other scientists. All of the vials are accounted for but Boone warns that the ZFT could duplicate his research and weaponize it. He can make a cure now that they have the dose samples. He insists he needs a lab, and Olivia says it won't be a problem.
Olivia takes Boone to the lab where Walter shows him around. Charlie calls in to reveal that they've found Dunn's missing car, abandoned and stripped. The GPS is gone and they have no way to determine where he picked up Valerie. Peter has a friend, Mako, who handles stolen cars and would know where the car's GPS might be. Olivia and Peter go to see Mako and get him to tell them where he found the car in Weymouth.
Walter and Boone infect a rat with the syphilis sample and try to make a cure using penicillin. Walter praises Boone on his intellect, and Boone admits he knows who Walter is. Boone wonders if he'll one day be judged and Walter notes he discussed the same thing with Bell. He admits there should still be time for redemption.
In Weymouth, Peter and Olivia find the spot where Mako found the car. Peter finds a corpse nearby with its spinal column ripped out.
At the lab, Boone and Walter prepare to inject the antidote into the infected rat. Olivia arrives with the bodies and the team determines all of the men have a stamp from the same bar, the Cavern. The rat dies and Boone warns he needs more time, but he needs them to capture Valerie alive so he can save her.
Valerie is at the Cavern when Peter and Olivia arrive with a handheld thermal imager to locate her higher body temperature.
Boone figures out that the cure needs some spinal fluid, and his own is the only type compatible. He thinks he still has enough to safely remove, but Astrid warns against it. Walter ignores her and orders her to prep Boone.
At the Cavern, Peter spots Valerie and he and Olivia move in. they lose her in the crowd. Olivia checks with Charlie outside, and he confirms no one has left.
Walter removes some of the spinal fluid from Boone.
Olivia spots Valerie and warns Charlie she's heading outside with a man. Charlie orders her to stop and when she refuses, they fire tranq darts and render her unconscious. Olivia sends word to the lab, but Astrid and Walter see that Boone is having a stroke. Walter realizes that Boone lied about how much spinal fluid he could spare.
Peter and Olivia drive toward the lab with Peter driving. He turns on the siren as they drive through traffic. They discuss Boone's love for his wife and Rachel's problems, but are interrupted when Valerie wakes up unexpectedly and attacks Olivia. Peter manages to tranquilize her again. At the lab, Walter administers the antidote and Valerie goes into convulsions then passes out. A few seconds later her eyes go back to normal and she's cured. However, Boone dies on the table. Walter gives Olivia a videotape that Boone made earlier. She plays it and Boone explains that he's keeping his bargain and gives her the names that he has.
Later, Olivia goes to a club and meets with Broyles. She reveals that Boone gave them the name of the man funding ZFT: William Bell.