The castaways on the raft are surprised at sea by something they didn't expect. Meanwhile, remaining islanders try to blow open the hatch, and a visitor to the encampment might be a threat to Claire's infant son,.

The castaways on the raft are surprised at sea by something they didn't expect. Meanwhile, remaining islanders try to blow open the hatch, and a visitor to the encampment might be a threat to Claire's infant son.

The French woman -- Rousseau -- shocks the survivors by showing up with a dire warning about "the others." Meanwhile, Michael and Jin ready the raft for sailing.

Jack suspects foul play when Michael becomes violently ill while building the raft. Meanwhile a secret from Kate's past is revealed, the mysterious hatch is shown to a few of the survivors, and Walt gives Locke a warning.

After burying one of their own, tempers flare as the castaways' suspicions of each other grow -- and an unlikely survivor vows revenge. Meanwhile, Claire and Charlie struggle to calm her newborn.

Claire goes into labor while a helpless Charlie goes into panic mode. Meanwhile Locke is missing, Jack tends to a wounded survivor and Sayid presents Shannon with a romantic surprise.

Boone becomes concerned when Locke suffers physical problems while they try to find a way into the mysterious hatch. Meanwhile, Jack is reluctant to help when Sawyer starts to experience excruciating headaches, and Michael and Jin struggle to communicate while working together on the raft.

When Hurley becomes obsessed with the French woman and heads into the jungle to find her, Jack, Sayid and Charlie have no choice but to follow. Meanwhile, Locke asks Claire to help build a mysterious item.

When the raft the survivors have been building mysteriously burns down, Michael is convinced that Jin is responsible for the sabotage, which only further escalates their rivalry. Meanwhile, Sun stuns her fellow survivors with a surprising revelation, and Boone gives Sayid a warning about Shannon.

Kate and Sawyer divulge dark secrets to each other while tracking a renegade boar that Sawyer swears is purposely harassing him. Meanwhile, Hurley and Sayid worry that Charlie is losing it after his brush with death, and a shocking, prior connection between Sawyer and Jack is revealed.

After the missing Claire returns with no recollection of what has happened since before the doomed flight of Oceanic 815, Jack and Locke formulate a plan of defense against her kidnapper, the mysterious Ethan, who threatens to kill off the other survivors unless Claire is returned to him.

Violence ensues and a mysterious island beast makes a re-appearance when Michael and Locke clash over Walt's upbringing. Meanwhile, Charlie is tempted to read the missing Claire's diary, and Sayid enlists Shannon to help decipher the French woman's map.

When Locke learns that Boone wants to tell their "secret" to Shannon, Shannon's life is placed in sudden peril, and the shocking truth about her past with Boone is revealed. Meanwhile, Kate is puzzled by Sun's mysterious behavior, and a hungry Hurley must repay a debt to Jin.

Jack, Kate and Sawyer fight over possession of a newly discovered locked metal briefcase which might contain insights into Kate's mysterious past. Meanwhile, Sayid asks a reluctant Shannon to translate notes he took from the French woman, a rising tide threatens to engulf the fuselage and the entire beach encampment, and Rose and a grieving Charlie tentatively bond over Claire's baffling disappearance.

Survivors wonder why Charlie and the pregnant Claire have been abducted - and by whom -- and a search party ventures into the treacherous jungle to try to find and rescue the missing duo. Meanwhile, inner-demons about his father resurface for Jack, and Boone and Locke discover another island mystery.

Jack, Kate and Charlie wonder if Claire's disturbing nightmares might be coming true to threaten her life and the life of her unborn child, and a missing castaway returns with frightening news about what lies just beyond the mountains.

Sayid's life is placed in grave danger after he stumbles upon the source of the mysterious French transmission. Meanwhile, Hurley has a ridiculous plan to make life on the island a little more civilized - and it just might work.

When Shannon suffers an asthma attack, Jack and Sayid realize brutality might be the only way to convince Sawyer to relinquish the life-saving medicine he's hoarding. Meanwhile, Sun struggles to decide if she'll obey husband Jin's orders to stay out of others' affairs, and Kate uncovers some shocking secrets about Sawyer.

Charlie begins a painful journey of withdrawal from drugs, surprisingly aided by Locke, whose true motive for helping Charlie is a mystery. Meanwhile, survivors struggle to find and free Jack when he's buried alive in a cave collapse, and someone might be secretly thwarting Sayid, Kate, and Boone when they enact a plan to find the source of the French transmission.

Walt and the others are shocked when Michael is brutally beaten, but only the non-English-speaking Jin and Sun know the truth behind the attack. Meanwhile Kate, Jack, Sawyer and Sayid argue about where the survivors should camp -- on the beach, where they're more likely to be seen, or in a remote inland valley where fresh water abounds; and Locke discovers Charlie's secret

Jack is near delirious from lack of sleep and struggles to overcome the haunting events that brought him to Australia and, subsequently, to the island. Meanwhile, Boone gets caught in a treacherous riptide, the pregnant Claire's health takes a bad turn, and a thief may have stolen the last bottles of water. Veronica Hamel.

Survivors are jolted awake in the middle of the night when wild island beasts invade the beach encampment. Kate and Michael join the mysterious Locke on a hunt for food -- and a shocking secret about Locke is revealed. Meanwhile, some survivors are horrified by Jack's plan for the dead bodies still scattered among the wreckage, and Jack sees someone in the jungle who might not have been on the plane.

Jack and Hurley discover an alarming secret about Kate, as the marshal's life hangs in the balance. Meanwhile Kate, Charlie, Sawyer, Sayid, Boone and Shannon ponder the island's mysteries they've uncovered and worry that telling the other survivors will cause panic, and Locke's befriending of Walt disturbs Michael.

The discovery of a transceiver among the plane's wreckage and the thought that rescue could be imminent temporarily raises the castaways' spirits. And the island's mysteries continue to baffle with the discovery of handcuffs, a gun and an animal that shouldn't be able to survive in a tropical climate.

Out of the blackness, the first thing Jack senses is pain. Then burning sun. A Bamboo forest. Smoke. Screams. With a rush comes the horrible awareness that the plane he was on tore apart in mid-air and crashed on a Pacific island. From there it's a blur, as his doctor's instinct kicks in: people need his help.