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.

Jack and Hurley discover an alarming secret about Kate, as the marshal's life hangs in the balance and he suffers a lot of pain. Meanwhile Kate, Charlie, Sawyer, Sayid, Boone and Shannon ponder the mysteries they have begun to uncover and worry that telling the other survivors will cause panic. They decide to lie for the time being. Also, Locke's befriending of Walt disturbs Michael, but Walt is more concerned in finding his dog. Lastly, Kate flashes back to when she was arrested by the marshal in Australia.

The French woman-Danielle Rousseau-shocks the survivors by showing up to the camp with a dire warning about "the Others" who are on the island, and the black smoke that precedes them. Meanwhile, Michael and Jin ready the raft for sailing. In flashbacks, we see the survivors final moments before they boarded their fateful flight.

The castaways on the raft are surprised at sea by something unexpected. Meanwhile, remaining islanders attempt to blow open the hatch, and a visitor to the encampment might be a threat to Claire's infant son.

As Kate’s backstory continues, her original crime is revealed. She thinks something is haunting her through Sawyer. Locke and Eko make an interesting discovery about the film, and Michael has a mysterious encounter with the computer.

Jack makes a decision regarding Ben's offer. Sawyer's life is placed in danger when Pickett decides to make good on his threat. Locke discovers a hidden message that may help unlock the island's secrets. Kate recalls memories from the past, which caused her to make an important choice.

Kate and Juliet are stranded in the jungle after Kate learns that there is a traitor in the survivor's midst. Meanwhile, Sawyer's poor attitude and selfish ways towards the beach community may earn him a vote of banishment if he doesn't have a change of heart.

Two outcomes of the detonation of the hydrogen bomb are presented. Flight 815 lands safely at LAX, where Kate escapes from the marshal and Jack learns that his father's body was lost in transit.

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.