Season 1, Episode 19:
The Road Not Taken
The Fringe team investigates the case of a woman who spontaneously combusts in the middle of a busy New York street. The team discovers that the victim is the subject of a ZFT experiment to cultivate pyrokinesis. As they investigate, Olivia experiences "visions" while awake. Walter suggests she is seeing an alternate universe which has branched off from our own. Olivia and Peter visit an agoraphobic website designer, who is apparently aware of William Bell, the drug trials, and the coming war, although his credibility comes into question when he also believes himself to be a character in Star Trek.
Using information from her visions, Olivia tracks down the victim's twin sister, just moments after she was kidnapped for more ZFT experimentation. Sanford Harris is revealed to be responsible for these crimes, and while closing in on him, Olivia gets locked in a room with the sister, whose unstable pyrokinetic abilities threaten both their lives. With Olivia's guidance, the woman focuses her energy on Harris and incinerates him. Olivia finds out that the sisters were part of the same nootropic drug trial that she was as a child. She presses Walter to reveal why he and William Bell were developing "super-soldiers," but Walter can only tell her that it was for protection against some impending doom that he regrettably cannot recall.
Meanwhile, Walter reveals that the ZFT manuscript was written by William Bell, and that the copy of the manuscript that ZFT uses is missing a chapter dealing with ethics. He locates the original, but the Observer shows up and takes Walter away, cryptically stating: "it is time to go." Nina Sharp visits Broyles to discuss the Observer, and is later shot in her hotel by two masked gunmen.
- Actor Allusion: Emmanuel Grayson, the conspiracy theorist Olivia and Peter visit, believes he's actually Spock from Star Trek: The Original Series. Not only is this a reference to Leonard Nimoy who plays Bell, Grayson is played by Clint Howard who also appeared on Star Trek.
- Amoral Attorney: Isaac Winters, the same guy who activated Nick Lane. Thankfully, Olivia puts him down for good.
- Call-Back: The Lights test appears once more, on the desk next to Nancy.
- Early-Bird Cameo: Olivia keeps catching glimpses of somewhere else. In one instant, she goes from seeing Boston being evacuated, and a military helicopter trying to keep order, to the regular skyline. It's the other universe.
- Kick the Son of a Bitch: Sanford finally crashes and burns.
- Tear Jerker: Olivia browbeating Walter until he breaks down in tears and sobbing that he can't remember what the Cortexiphan trials were for. This performed a double role of making Walter more sympathetic whilst portraying Olivia in a less-than-stellar light (even if she had good reason for the anger).
- What the Hell, Hero??: Olivia finally calls Walter out on the Cortexiphan Trials, but Walter can't even remember WHY they did it on the first place.