In the episode, Daniel Faraday (Jeremy Davies) returns to the Island in order to warn the inhabitants of a catastrophe involving the DHARMA Initiative research station the Swan.

In flashbacks, Daniel's relationship with his parents, Eloise Hawking (Fionnula Flanagan) and Charles Widmore (Alan Dale), is shown.

Years later, following the crash of Flight 815, Daniel has suffered severe psychological effects from performing experiments on himself; he has lost his mental acuity, and now lives with a caretaker.

Following the events of the previous episode, "Some Like It Hoth", Daniel has returned to the island, having spent three years in Ann Arbor, Michigan, conducting research for the Dharma Initiative.

At the Barracks, Sawyer, Juliet, Jin (Daniel Dae Kim), Hurley and Miles decide that they will flee to the survivors' original beach, abandoning Dharma.

They arouse suspicion from Dharma's head of research, Radzinsky (Eric Lange), while trying to steal weapons, and a gun fight ensues.

The survivors are able to escape; however, Radzinsky brings his team to Sawyer and Juliet's house, where they find Dharma member Phil (Patrick Fischler) tied up.

Meanwhile, Daniel explains to Jack and Kate that he intends to detonate the hydrogen bomb that had been buried on the island in 1954 in order to prevent the construction of the Swan, which in turn will ensure that Oceanic Flight 815 never crashes on the island, which means it never becomes visible to Widmore's team, so he never sends the freighter which brings himself and Charlotte, therefore Charlotte does not die.

"[4] Since Lindelof and his show runner partner Carlton Cuse wrote "The Constant", they thought the "sister episode" should be written by someone other than them, which led to Kitsis and Horowitz writing it.

However, his quiet demeanor and seemingly good heart made him a favorite with the fans, so Lindelof and Cuse decided to expand Daniel's role, which has led to him being a key player in Lost's eventual resolution.

"[7] Once the show runners explained that to Davies, he was saddened that his full-time status on Lost was coming to an end, but put the story "above his own personal self".

Josh Holloway, who plays the role of Sawyer, said, "Just statistically speaking, to hit a hundred episodes doesn't happen very often, especially on a show where everyone is saying 'Lost on an island?

"[8] In an interview with The News & Observer, Lindelof recalled meeting with the ABC executives in 2004 to pitch the idea of a plane crash and survivors stranded on an island full of mystery and danger.

Lindelof added that if he had "traveled back in time to tell myself after that meeting that we were going to make it to a hundred and still have a season beyond that, I would have laughed in my face.

The cake featured replicas of a Dharma beer bottles, the computer from the Swan station, a suitcase and a miniature Oceanic Flight 815.

Lost was that Wednesday's number one scripted television show in the aforementioned demographic for its thirteenth straight original telecast.

[11] Since airing, the episode has received generally positive reviews from television critics, mostly complimenting Davies's performance as Daniel.

Chris Carabott of IGN commented that if this is the last appearance of Davies on Lost, which he "somehow" doubts, then, "I'm glad he had the opportunity to leave on such a strong note.

"[12] Rachel Dovey of Paste said the episode revealed "a whole different" side of Daniel: "We've oscillated before about the true nature of the physicist, whether it's good or evil [...] We decided he's mostly a decent guy, barring the whole experimenting-on-his-girlfriend-then-running-away-when-her-brain-turned-to-mush thing.