Her şeyden yoksun bırakılan 48 kazazede, hayatta kalmak için uçaktan ne bulabilirlerse toplarlar. Bazıları paniğe kapılırken, bazıları kurtarma umudunu gözetir. Birkaçı, hiç bilmedikleri iç gücü bulurlar - mesela Kate, tıbbi eğitimi olmadan aniden doktorun yaralarını dikerken kendini bulur. Arkadaşlar, aile üyeleri, düşmanlar ve yabancılar birlikte acımasız hava koşullarına ve zorlu araziye karşı çalışmak zorundadırlar. Ancak ormanda dolaşan gizemli yaratıkların yoğun ulumaları hepsini korkuyla doldurur. Neyse ki, hızlı düşünen Jack'in sakin liderliği ve sağduyulu Kate'in sayesinde umutları vardır.

"Yaratığın" elinden kaçan ve uçak telsizini geri alan bir grup kurtulan, sinyal iletebilmek için daha yüksek bir noktaya seyahat eder. Yolculukları sırasında gizemli bir ileti alırlar ve adanın diğer bir sakiniyle karşılaşırlar. Bu arada Jack, kamp alanında Kate hakkında bir sırrı ortaya çıkaran yaralı bir adamla ilgilenir.

Jack ve Hurley, Kate hakkında endişe verici bir sırrı keşfederler, çünkü marşalın hayatı dengede durmakta ve çok acı çekmektedir. Bu arada, Kate, Charlie, Sawyer, Sayid, Boone ve Shannon, ortaya çıkarmaya başladıkları gizemleri düşünüp, diğer kurtulanlara söylemenin paniğe yol açabileceği endişesi taşırlar. Şimdilik yalan söylemeye karar verirler. Ayrıca, Locke'un Walt ile arkadaş olması Michael'ı rahatsız eder, ancak Walt, köpeğini bulma konusunda daha endişelidir. Son olarak, Kate, Avustralya'da marşal tarafından tutuklandığı zamanlara geri döner.

Kurtulanlar vahşi ada yaratıkları (yaban domuzları olduğu ortaya çıkan) plaj kampına saldırdığında gece ortasında uykularından sıyrılırlar. Kate ve Michael gizemli Locke ile birlikte yiyecek bulmak için avlanmaya çıkarlar ve Locke ile ilgili şok edici bir sır ortaya çıkar. Yiyecek arayışında birisi yaralanır. Bu sırada, bazı kurtulanlar Jack'in enkazlar arasında hala dağılmış olan cesetleri yakma planından dehşete düşer. Jack orada olmayan birini görür ve bir kurtulanın daha önce yürüyemeyen fakat şimdi yürüyebilen biri olduğunu öğreniriz.

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.

Shannon's inhaler runs out and Boone believes Sawyer has the remaining three in his stash. When Sawyer refuses to give them up, Jack and Sayid resort to torturing Sawyer until he agrees to reveal the location of the inhalers. In flashback we hear Sawyer's story and find he is not who he says he is.

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.

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 kidnapping.

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.

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.

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.

Kate and Sawyer divulge dark secrets to each other while tracking a renegade boar that Sawyer swears is purposely harassing him. Hurley and Sayid worry that Charlie is losing it after facing a brush with death and killing Ethan with 6 bullets to the chest. A shocking prior connection between Sawyer and Jack is revealed in a flashback which shows Sawyer meeting Jack's father in a bar. Robert Patrick ("Terminator 2: Judgment Day," "The X-File") guest stars.

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.

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. Hurley flashes back to the hugely life-altering experience he had before boarding the plane.

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.

Jack tends to a severely wounded Boone after Locke returns him to the caves. In the confusion, Locke slips away to deal with his guilt over the crisis. Meanwhile, Claire unexpectedly goes into labor while deep in the forest.

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.

Jack suspects foul play when Michael becomes violently ill while building the raft. The suspects include Sawyer and Kate, who compete for the last seat on the raft and do anything possible to prevent each other from getting it. Meanwhile, a secret from Kate's past is revealed to the other survivors on the island.

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.