Kate discovers that someone knows the secret of Aaron's true parental lineage. Meanwhile, the dramatic shifts through time are placing the lives of the remaining island survivors in extreme peril.

Suspicions about a possible breach intensify after Ben is taken from the infirmary, and a reluctant Miles is forced to work with Hurley when he's asked to deliver an important package to a top Dharma official.

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.

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.