Fringe/Recap/S01 E11

Season 1, Episode 11:

Bound
The ZFT scientists extract some spinal fluid from Olivia, but before they can do anything else, she escapes and makes contact with the FBI. However, when agents come to collect her, they use tranquilliser guns to sedate Olivia before bringing her to see Sanford Harris, an internal affairs investigator with a grudge against Olivia who has been brought in to check Fringe Division's conduct. Meanwhile, an epidemiologist is killed when something slug-like grows inside him and slithers out of his mouth. When the team investigates, Walter discovers the slug is actually a single giant cell of the common cold virus. They take another epidemiologist into protective custody, but Mitchell Loeb slips another parasite into his drink.

During the investigation, Olivia spots a clue that makes her realise Loeb was one of her abductors. She goes to his house to try and gather evidence and is discovered by Loeb's wife. In a shootout, the wife is killed and Olivia discovers evidence that links Loeb to the death of the epidemiologists. Loeb is arrested and Olivia coerces him into confessing to the kidnapping and the murders: Loeb claims that Olivia's abduction was for her own benefit, and the ZFT was trying to help her.