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

When Sawyer escapes from the temple, Kate and Jin are sent to bring him back. Meanwhile, the Others determine Sayid is infected and attempt to poison him. In the flash sideways, Kate, still on the run, takes Claire to a hospital when she goes into labor.

On the island, the Man in Black attempts to recruit Sawyer in his attempt to leave the island, while an impromptu funeral is held for the real Locke. In the flash sideways, Locke is fired from his job and becomes a substitute teacher.

On Jacob's orders, Hurley leads Jack to a lighthouse. Meanwhile, Claire questions an Other she has captured while tending to an injured Jin. In the flash sideways, Jack is a single father trying to bond with his son.

After recruiting Sayid to his cause, the Man in Black issues an ultimatum to the Others: either join him or die. Meanwhile, Kate is reunited with Claire. In the flash sideways, Sayid helps his brother, who is in debt to a loan shark.

Ilana discovers Ben killed Jacob, so she plans to kill him. Meanwhile, Jack, Hurley and a suicidal Richard visit the Black Rock. In the flash sideways, Ben, a high school teacher, tries to blackmail the school's principal.

The Man in Black sends Sawyer on a reconnaissance mission to Hydra Island, where he discovers that Charles Widmore has returned to the island with a team of scientists. In the flash sideways, Sawyer is a lonely cop who is still searching for the original Sawyer.

Richard Alpert's back story is shown: In 1867, he is brought to the island on the Black Rock as a slave. He makes a deal with Jacob to be his representative in exchange for immortality. In the present day, Hurley convinces him to help the candidates replace Jacob and stop the Man in Black from leaving the Island.

After Jin is kidnapped and taken to Hydra Island by Widmore's team, the Man in Black confronts Widmore. On the main island, Sun loses her ability to speak English. In the flash sideways, Sun and Jin are abducted after failing to complete a transaction for Sun's father.

On the island, Widmore subjects Desmond to a large amount of electromagnetic energy as an experiment. In the flash sideways, Desmond, with the aid of Charlie, starts to have visions of his life in the original timeline.

In order to prevent more loss of life, Hurley leads the other survivors to speak with the Man in Black. In the flash sideways, Hurley meets Libby, while Desmond continues his mission to let the Oceanic 815 passengers know of their lives on the island.

The survivors split into two groups; one led by Sawyer, the other by the Man in Black. Sawyer's group travels to Hydra Island, where they are captured by Widmore's crew after Sun and Jin are reunited. In the flash sideways, the passengers of Oceanic 815 continue to cross paths with each other.

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.

When Claudia, a heavily pregnant woman, washes ashore, support is at hand in the form of a stranger. But her intentions for Claudia and the unborn twins are unknown.

Jacob appears to the survivors of the submarine explosion and tells them what they were chosen for. Ben joins forces with Locke, as they both have a final showdown with Charles Widmore.

On the Island, Jack and the Man in Black play out their last moves as the survivors make their final choices, and the true nature of the flash sideways is revealed.