A parallel universe, in which the crash never happened, is revealed as an aftermath of the bomb's detonation. Meanwhile, Sawyer blames Jack for the loss of Juliet and the true identity of the monster is revealed.

Jack, Sawyer, Kate, Miles and Hurley, struggling to save Sayid, face an ancient secret. Meanwhile, a fake Lock exits the chamber to everyone's awe.

Kate finds herself on the run, while Jack is tasked with something that could put a friend's life at risk.

Locke goes in search of help to further his cause. Kate finds herself on the run, while Jack is tasked with something that could put a friend's life at risk.

Hurley must convince Jack to accompany him on an unspecified mission, and Jin stumbles across an old friend.

Sayid is faced with a difficult decision, and Claire sends a warning to the temple inhabitants.

Ben deals with the consequences of an uncovered lie.

Locke tasks Sawyer with a mission.

Richard Alpert faces a difficult choice.

Sun and Jin desperately continue their search for one another, and Locke confronts his enemy.

Desmond wakes up to discover he's back on the island.

Hurley worries about what the group should do next and Locke is curious about the new arrival in his camp.

Alliances are forged and broken as the Locke and Jack camps merge.

After the remaining survivors are reunited, Sawyer and Jack hatch a plan to divert the Man in Black's attention and leave the island without him on Widmore's submarine, but disastrous consequences await them. In the flash sideways, Jack investigates the cause of Locke's paralysis and offers treatment.

The motives of John Locke are finally explained.

While Locke devises a new strategy, Jack's group searches for Desmond.

Jack, the new protector of the island, meets with Locke and they go past the bamboo field with Desmond to visit the heart of the island. The Man in Black's final fate is determined, and one survivor must make the ultimate sacrifice to save the island. Meanwhile, in another life, the ones who might have been the survivors gather for a final time.

The Man in Black's final fate is determined, and one survivor must make the ultimate sacrifice to save the island. Meanwhile, in another life, the ones who might have been the survivors gather for a final time.