Stripped of everything, the 48 survivors scavenge what they can from the plane for their survival. Some panic. Some pin their hopes on rescue. A few find inner strength they never knew they had-like Kate who, with no medical training, suddenly finds herself suturing the doctor's wounds. The band of friends, family, enemies and strangers must work together against the cruel weather and harsh terrain. But the intense howls of mysterious creatures stalking the jungle fill them all with fear. Fortunately, thanks to the calm leadership of quick-thinking Jack and level-headed Kate, they have hope. But even heroes have secrets, as the survivors will come to learn.

Having escaped the "creature" and retrieved the plane transceiver, a group of the survivors travel to higher ground so they can transmit a signal. En route, they receive a mysterious transmission and encounter another of the island's inhabitants. Meanwhile, back at camp, Jack tends to a wounded man who reveals a secret about Kate.

Hurley struggles with an assigned task inside the hatch as he flashbacks to disturbing memories in his life before the crash. Meanwhile, Sawyer, Michael and Jin learn the identities of their captors on the island. Claire uncovers a startling piece of information about the fate of the raft.

Michael sets off into the jungle by himself determined to find Walt, but discovers that he is not alone. Meanwhile, Sawyer and Jin are ordered by their captors to take them to their camp, and Sun frantically searches for her missing wedding ring. In flashbacks this episode reveals more of Jin's life before ending up on the island.

Sawyer's wound becomes life threatening as he, Michael and Jin make their way through the interior of the island with the tail section survivors.

The harrowing first 48 days in the lives of the tail section survivors are revealed. Flashbacks reveal the point of view of Ana-Lucia, Mr. Eko, Bernard and Libby and other survivors as they landed on the other side of the island on the beach. As the days progress danger hits their camp as well when "The Others" start taking people against their will...

As Kate and Sawyer journey back to the main island with Karl, who is exhibiting effects of the brainwashing video, they argue over whether to go back and save Jack. On Hydra island, as Juliet's fate rests in his hands and a power struggle within the Others ensues, Jack recollects the time he spent in Phuket, Thailand and his relationship with Achara, a mysterious tattoo artist.

After abandoning the Others, Locke takes Sawyer on a trek through the jungle to help him eliminate a common enemy. Meanwhile, back at the beach, the parachutist Naomi has crucial information about flight 815.

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.

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

Locke tasks Sawyer with a mission.

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