FROM ENTERTAINMENT REPORTER KIMBERLY ROOTS: We open on a sketchy-looking, smooth-talking British guy getting ready to go out for the night. A TV news report in the background alerts us to a murder that seemed to have been committed with a knife. Just then, we see the Brit pick up a folding knife and put it in his pocket. So he’s the killer! He goes to a nightclub and calls his girlfriend, who’s traveling, before going in. He lies about spending a quiet night alone, then steals into the club and unsuccessfully puts the moves on one woman before hitting it big with another. They go back to his apartment … where she kisses him and then breaks his neck in one quick movement. Later we see him with his spinal column sliced open. So she’s the killer—nice fake-out, Fringe.
Charlie, Olivia, and the Bishops arrive on the scene the next morning. The murder method matches the one on the news the night before, but the stymied Boston police are handing it over to the FBI. Walter says the wound was made by human teeth and later deduces that the killer nabbed the victim’s spinal fluid. To rachet up the ick factor, lab tests from the wound show that the killer had traces of an extinct kind of syphilis in his or her saliva. The Centers for Disease Control are the only ones who have samples of the virus, and the CDC points Olivia in the direction of Luboff Pharmaceuticals: Luboff has received several samples that could be used in bioweapons. Olivia and a strike team storm the lab and find a wheelchair-bound man poking around a dead animal’s spinal column. They bring the man, Nicholas Boone, in for questioning and ask how long he’s been a follower of ZFT. Boone looks surprised for a minute, but then says he will help them if they will find his wife. He worked for the people they’re looking for, he continues, but when he realized what “they”—presumably those perpetrating the "pattern"—were up to, he tried to pull out. That’s when they kidnapped his wife, Valerie. Boone also lets Olivia and company know that he created the skin-growth virus that killed an FBI agent a few episodes back.
Boone sends Olivia and a team on a raid of another secret lab, where they don’t find his wife, but do locate some vials of a substance called XT43. “The person who’s killing has been dosed with this,” he says, adding that he needs it to make an antidote. Then he comes clean: “They didn’t kidnap my wife. They infected her.” Elsewhere, we see his wife making eyes at the bouncer at a club. They go back to his car, where he touches her face and notices that she’s burning up. She mutters, “I’m sorry,” before rearing back, baring rows of razor-like teeth and then launching herself at his neck.
Boone's wife is now feeding off spinal fluid; it’s why she kills, and his attempts to keep her satiated by drinking his left him paralyzed. He asks for a lab to synthesize the antidote and winds up at Walter’s. Boone eventually realizes that even more of his spinal fluid is necessary to make the cure, so he lies to Walter about having enough to spare. Meanwhile, ultraviolet stamps on several victims’ hands lead Olivia and Peter to the club where Valerie’s been hunting her prey. They tranquilize her and transport her back to the lab, where Boone is not doing well. They inject Valerie with the antidote just as her husband dies on the stretcher next to her.
Later, Walter hands Olivia a videotape Boone left for her. Making good on his promise, he leaves a message that says he doesn’t know much about ZFT except this: The man bankrolling the movement is Massive Dynamics chief—and Walter’s former lab partner—William Bell.
THE BOTTOM LINE: During a quiet moment in the lab, Walter and Nicholas Boone have this telling exchange, with echoes of one of science-and-religion’s central conflicts:

WALTER: A little memory loss is often kind to the soul.

NICHOLAS: A figure of speech, or do you believe there is such a thing? The soul?

WALTER: There are days when I wish I did. There are days when I wish I didn’t.

NICHOLAS: I often wake up at night, frightened, with the understanding that there are things man shouldn’t know. That the scientific trespasses I’ve committed —

WALTER: — will one day be judged. Bellie and I would often debate this kind of thing. William Bell. You’ve heard of him?