Olivia (Anna Torv) experiences a strange disturbance in her home that creates a brief time distortion and attracts metallic objects to it before it dissipates.
Walter, observing this from his lab, surmises the effects are similar to one of his Cortexiphan children test subjects who displayed the ability for astral projection.
Walter suspects the children who underwent the Cortexiphan nootropic drug trials are psychically linked, which is why Olivia is experiencing them.
While there, it is revealed to the viewer that, in this alternate timeline, the Cortexiphan trials were stopped after Olivia ran away from experiments as a child (à la Subject 13 but without Peter (Joshua Jackson) to bring her back).
As they try to figure out what to do next, Olivia receives a call from Broyles (Lance Reddick), explaining that they have come across a man who had just appeared in Reiden Lake and who knows far too many confidential details about Fringe.
[2] Leading up to the episode's broadcast, actress Anna Torv noted that "Subject 9" is when "all of the little bits and pieces come into place – especially regarding the whole question of 'When is Peter Bishop going to make an appearance?
'"[3] She expressed appreciation that her character Olivia was able to grow closer to Walter due to Peter's absence, noting that this was her favorite part of the episode.
[1] Walter tells Olivia that his inspiration for setting up the cameras came from "the fight sequences in The Matrix", a 1999 science fiction action film.
"[4] Andrew Hanson of the Los Angeles Times noted of the various timelines depicted in the series, "With any other show, this might have driven the audience crazy, but Fringe pulls it off.
[4][9] Charlie Jane Anders of io9 believed that it was "the first truly great episode of Fringe season four, and one which gave me a lot of hope," explaining that "the show finally refocused back onto the elements that made it essential viewing in the past, in particular the tangled legacy of Walter Bishop.
"[10] Writing for SFX magazine, Richard Edwards expressed pleasure with Peter's return, though he thought it was "almost too easy, seemingly the result of a series of fortunate events and Olivia’s intuition rather than any grand plan...