After reading about the death of someone he knew, Jack prepares to commit suicide by jumping off the Sixth Street Viaduct bridge.

[4] Sayid Jarrah (Naveen Andrews), Jin Kwon (Daniel Dae Kim), and Bernard Nadler (Sam Anderson) remain at the beach, tasked with igniting the dynamite while the rest of the survivors go with Danielle Rousseau (Mira Furlan) to the radio tower to communicate with Naomi Dorrit’s (Marsha Thomason) nearby ship.

[5] After hearing only two explosions, James "Sawyer" Ford (Josh Holloway) and Juliet Burke (Elizabeth Mitchell) go back to the beach.

Hugo "Hurley" Reyes (Jorge Garcia) drives the van he found onto the beach,[6] and the captives gain the upper hand, killing the remaining Others with the help of Sawyer and Juliet.

Charlie Pace (Dominic Monaghan) is captured by the resident Others Greta (Lana Parrilla) and Bonnie (Tracy Middendorf).

Ben Linus (Michael Emerson) learns of Charlie's infiltration and sends Mikhail Bakunin (Andrew Divoff) to the station to kill them to protect the signal jammer.

Mikhail arrives and kills Greta and Bonnie, but is shot with a spear gun by Desmond Hume (Henry Ian Cusick) who hid in the station after diving down after Charlie.

Getting the code from Bonnie before she dies (the notes to the middle eight of "Good Vibrations" by The Beach Boys), Charlie disables the jammer and is contacted by Penny Widmore (Sonya Walger) through video transmission.

[18] Despite not being mentioned in the official press release,[19] then-15-year-old Malcolm David Kelley, who was a main cast member in Season 1, returned to reprise his role as 10-year-old Walt Lloyd,[20] and received credit as a "special guest star".

[23] The producers had hoped that Harold Perrineau, who plays Walt's father Michael Dawson, would return in this episode, but he was filming the pilot for CBS' Demons.

[35] After Lindelof and Cuse wrote the scene, only Fox, Lilly, Bender, and co-executive producer Jean Higgins were given copies of the script.

[42] With the announcement that the series would conclude 48 episodes after "Through the Looking Glass",[43] they felt comfortable playing flashforwards as early as the third-season finale.

[48] Buena Vista Home Entertainment released "Through the Looking Glass" on the season's DVD and Blu-ray Disc sets on December 11, 2007, in Region 1.

[49] A featurette called "Lost: On Location" features cast and crew discussing production of select episodes, including "Through the Looking Glass".

[56] In the United Kingdom, the episode attracted 1.21 million viewers, and was the second most watched program of the week on the non-terrestrial channels, beaten only by Katie & Peter: The Next Chapter.

[61] The Los Angeles Times wrote that the episode was "an unusually action-packed and sanguinary spring cleaning that… left a host of… characters… dead",[62] Access Atlanta said "it was deeply satisfying.

"[64] The San Francisco Chronicle wrote that "not only was the pace fast, the teases taut, and the answers plenty, the writers took a compelling gamble… [by telling] viewers that in the future… maybe all… of the people on the Lost island get off.

"[66] The Pittsburgh Post-Gazette commented that the flashforward "twist gave the saga renewed momentum as it begins its march toward a 2010 finish.

"[67] The season finale was summed up as "a mind-blower, for sure, a radical two hours that gave us major fake-outs, an army of dead bodies, the possibility of rescue [and] diverse portraits of heroism" by The Boston Globe, who added that the death of Charlie was "the most touching loss of the series so far.

[70] The Chicago Tribune called it "a qualified success" with excellent pacing and action, however, the flashforward scenes were thought to be uninteresting and "clumsy".

"[41] TV Guide described "Through the Looking Glass" as "a dizzying exercise in adventure, sustained tension and time-shifting rug pulling [that was] spectacularly produced, amazingly directed and gloriously acted.

"[75] IGN gave the double episode a perfect 10/10[76] – the best review of the season – saying it was "nothing short of a masterpiece of storytelling with a brilliantly paced narrative.

[83] AOL's TV Squad gave the episode a 7/7, noting that "the writers followed through on Desmond's premonitions and successfully delivered the highly anticipated game-changer.

"[86] Entertainment Weekly ranked it as one of the top ten episodes of 2007,[87] saying that the cliffhanger "[revealed] new dimensions to [Lost's] creative world.

"[90] Lindelof stated "that we might be willing to give [Locke] the benefit of the doubt for any action he took in response to [lying, gut shot, in a pit of Dharma corpses for two days and on the verge of taking his own life], even if considered slightly 'out of character'.

[96] For his work on this episode, Jack Bender was nominated for the Directors Guild of America Award for Outstanding Directing – Drama Series.