Jack is nearly 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 trying to save a woman who went out swimming. A pregnant Claire's health takes a bad turn from lack of fluids, and a thief may have stolen the last bottles of water. Veronica Hamel guest-stars as Jack's mother, Margo.

Also, Jack flashes back at 12 years old, to find himself on the playground in an altercation with a bully, who ultimately beats him up, and later learns a life lesson from his father.

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.

Sayid's life is placed in grave danger after he stumbles upon the source of the mysterious French transmission, the woman Danielle Rousseau (guest-star Mira Furlan). She was on the distress call and is found alive. Meanwhile, Hurley has a ridiculous plan to make life on the island a little more civilized. The plan involves golf clubs he finds in the debris, and it looks like it just might work. Lastly, we flash back to Sayid's childhood friend Nadia as well as his participation in hostage situations in Iraq.

Claire has a horribly realistic nightmare about her new baby being harmed or kidnapped. Flashbacks reveal Claire's backstory: the former boyfriend who got her pregnant, then abandoned her, and the psychic who convinced her to take the ill-fated flight that landed her on the island. Hurley is shocked and confused when he discovers that Ethan Rom (guest-star William Mapother), another plane crash survivor, does not appear on the flight manifest.

Survivors wonder why Charlie and Claire have been abducted - and by whom - and a search party ventures into the treacherous jungle to look for the pair. Suspicions focus on Ethan Rom (guest-star William Mapother), who, it was recently discovered, was not a passenger on the doomed flight. Jack battles inner demons relating to his father, while Boone and Locke discover another island mystery.

When Locke learns that Boone wants to share their "secret" with Shannon, Locke decides to teach him a lesson. This leads to Shannon's life being placed in what seems like peril. Boone and Shannon's dark past is revealed in a shocking backstory that recalls their relationship right before the plane crash and presages the return of the beast. Kate, who has become a confidante to the soft-spoken Sun, is puzzled by Sun's mysterious behavior and the revelation that she can speak English. A hungry Hurley must convince Jin to share his fish by making up for offending Jin by rejecting his offer of raw fish early on, or he'll continue to suffer digestive problems from the limited island diet.

After the missing Claire returns with no recollection of what has happened since before she boarded the doomed Oceanic flight 815, Jack and Locke formulate a plan of defense against her kidnapper, the mysterious Ethan (guest-star William Mapother), who threatens to kill off the other survivors one by one unless Claire is returned to him. Meanwhile, the disappointment Charlie feels when Claire does not remember him triggers recollections of a woman he had let down in the past.

When the raft the survivors have been building mysteriously burns down, Michael is convinced that Jin is responsible for the sabotage, which only serves to escalate their rivalry. Meanwhile, Sun stuns her fellow survivors with a surprising revelation, and Boone gives Sayid a warning about his step-sister Shannon. Lastly, more details of Jin and Sun's troubled marriage are revealed through flashbacks.

Locke thinks he's being sent a sign on how to get the hatch open, and he and Boone venture inland. Jack is reluctant to offer assistance when Sawyer begins to experience excruciating headaches and needs glasses.

After another funeral, tempers rise as the survivors' suspicions of each other grow, and an unlikely survivor vows revenge. The events that landed Sayid on Flight 815 play out as he engages Locke in a psychological game of cat and mouse to uncover the truth about the mishap that claimed Boone's life.

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.

Jack, Locke and Kate explore the mysterious hatch but Jack decides to wait before going down into the hatch. Kate and Locke aren't so patient. When Shannon chases after Vincent the dog, she encounters a familiar face in the jungle.

Jack, Locke and Kate learn more secrets about the hatch. Meanwhile, after being beaten and taken captive, Sawyer, Michael and Jin wonder if their captors are fellow survivors or the dreaded "Others." Flashbacks reveals more of Locke's past in this episode as well as the introduction of Helen (guest star Katey Segal) who shakes things up even more with her revealing personality and past.

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.

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 the survivors race inland, trying to stay a step ahead of The Others, they realize that someone among them wasn't on Flight 815.

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, Locke and Sawyer follow after a determined Michael after he heads into the jungle toward the dreaded "Others" in search of Walt. Meanwhile, Sun has a surprising reaction to Jin's desire to join the search party, and Hurley and Charlie commiserate over the age-old conundrum of "what women want."

Some of the island survivors fear that "The Others" may have returned when Sun is greatly injured during a failed kidnapping attempt at her plant garden. Also, the trust barrier becomes very thin between Locke and Jack in terms of locking up the guns and being kept safe. Meanwhile, Sawyer is an amused but highly interested bystander when tension escalates between Jack, Locke, Kate and Ana Lucia. When Jack purposely takes Sawyer's medication from him he pushes more in favor of helping Locke. Lastly, flashbacks reveal more of Sawyer's con artist past.

A mysterious illness that baby Aaron suddenly contracts sends a desperate Claire, Kate and French woman Danielle to return to the same area where Claire was initially kidnapped. It is there where she believes she can find a cure for Aaron's illness. In the meantime, Jack and Locke are doing their best to keep their prisoner a secret from the rest of the survivors on the island.

When the hatch suddenly takes on a life of its own, Locke is forced to enlist the help of an unlikely ally to control the matter. Meanwhile, Ana Lucia, Sayid and Charlie go off into the jungle to find out the truth about Henry Gale and see if there really is balloon craft out there in the jungle that carried him and his wife to the island.

Rose is surprisingly and vehemently opposed to Bernard's plan to create an S.O.S. signal; romantic sparks are rekindled between Jack and Kate when they trek into the jungle to propose a "trade" with "The Others"; and Locke begins to question his faith in the island.

Mr. Eko has dreams about his brother leading him somewhere. He seeks Locke's help in finding a secret location, the "question mark." Meanwhile, Jack and the other survivors grapple with the horrific situation in the hatch with the death of Ana-Lucia and Libby clinging to life.

After discovering something odd just offshore, Jack and Sayid come up with a plan to confront "The Others" and hopefully get Walt back. At the same time there will be an answer to the question of where Michael has been and resolution of him and Walt. Meanwhile, Eko and Locke come to blows as Locke makes a potentially cataclysmic decision regarding the "button" and the hatch. Lastly, Desmond returns and he sheds some more light on his experience on the island in the three years prior to when Locke came down into that hatch.

After discovering something odd just offshore, Jack and Sayid come up with a plan to confront "The Others" and hopefully get Walt back. Meanwhile, Eko and Locke come to blows as Locke makes a potentially cataclysmic decision regarding the "button" and the hatch.