After a plane crash leaves 48 people stranded on an island, the survivors hope for a quick rescue, only to learn the island holds deep, dark secrets.
Having retrieved the plane transceiver, a group of survivors tries to transmit a signal, only to receive a strange message from another inhabitant.
Jack and Hurley discover an alarming secret about Kate, and the marshal's life hangs in the balance.
Wild beasts invade the beach camp, while Kate and Michael join Locke on a hunt for food.
A sleep-deprived Jack struggles to overcome the haunting events that brought him to the island, while Boone gets caught in a treacherous riptide.
Language barriers keep the group from knowing how Michael was brutally beaten. Kate, Jack, Sawyer and Sayid argue about where to camp.
Charlie begins his withdrawal journey with help from Locke. Meanwhile, Jack is buried alive in a cave collapse.
When Shannon's inhaler runs out, Sawyer refuses to give up his spares, leaving Jack and Sayid to use their own means of persuasion.
Sayid's life is in danger after finding the source of the French transmission, while Hurley hatches a ridiculous plan to make life more civilized.
Claire has a horribly realistic nightmare about her baby being harmed and recalls her life before the island.
A search party looks for Charlie and Claire in the jungle. Jack reflects on his relationship with his father.
Jack, Kate and Sawyer fight over a briefcase that might contain clues about Kate's past. Sayid asks Shannon to translate notes from the French woman.
When Locke learns that Boone wants to share their secret with Shannon, Locke plans to teach him a lesson.
A mysterious island beast reappears when Michael and Locke clash, while Sayid enlists Shannon to help decipher the French woman's map.
Claire returns with no recollection of the crash. Jack and Locke form a plan against her kidnapper, who makes threats toward the other survivors.
Kate and Sawyer divulge dark secrets while tracking a renegade boar. Hurley and Sayid worry about Charlie after his brush with death.
Michael accuses Jin of sabotaging the raft, while Sun stuns everyone with a surprising revelation.
Jack, Sayid and Charlie follow Hurley into the jungle, where he recalls a life-altering experience before the crash.
Locke thinks he knows how to get the hatch open, and he and Boone venture inland. Meanwhile, Jack is reluctant to help Sawyer get glasses.
Jack aids a wounded Boone, while Locke deals with his guilt. Deep in the jungle, Claire braces herself for the baby.
After another funeral, tempers flare, suspicion grows and a survivor vows revenge. Sayid engages Locke in a game of cat and mouse.
When Michael falls seriously ill while building the raft, Jack suspects foul play from Sawyer and Kate — who will do anything to get the last seat.
Rousseau shows up to camp with a dire warning about The Others and the black smoke, telling the survivors they need to run, hide... or die.
After the raft leaves, the remaining survivors scramble to flee the black smoke, while Claire panics, knowing that The Others are after her baby.
As Sawyer and Michael argue on the raft, the survivors try to blow open the hatch. The passengers remember their final moments before the flight.
Jack, Locke and Kate explore the mysterious hatch, while Shannon chases after Vincent the dog and encounters a familiar face in the jungle.
Michael and Sawyer fight for their lives on the high seas and discover a new predator. On land, Locke descends into the hatch to find a missing Kate.
Jack, Locke and Kate learn more about the hatch. Sawyer, Michael and Jin wonder if they've encountered The Others.
Hurley struggles with a task inside the hatch as he has a disturbing flashback. Sawyer, Michael and Jin learn their captors' identities.
Michael goes into the jungle to find Walt. Sawyer and Jin's captors demand to be taken to the camp.
Sawyer, Michael and Jin make their way through the island interior with the tail-section survivors.
The tail-section survivors recall their harrowing first 48 days after the crash.
Violence erupts when Ana Lucia and her group hold Sayid and the other castaways captive.
Kate wonders if something is haunting her through Sawyer. Locke and Eko make a discovery about the film.
Claire loses faith in Charlie after Eko asks him about the Virgin Mary statue. Kate gives Sawyer a much-needed haircut.
Jack, Locke and Sawyer follow a determined Michael as he heads into the jungle in search of Walt.
Charlie's vivid dreams lead him to believe Aaron is in danger, and Locke suspects he's relapsed. Sawyer encourages Hurley to make a move.
After Sun gets injured, some of the survivors worry that The Others have returned.
Suspicion grows as the survivors consider that one of their own might be an Other. Sawyer loses trust in Hurley.
When baby Aaron contracts a mysterious illness, a desperate Claire, Kate and Danielle try to find a cure.
Locke calls in Ana Lucia to interrogate Henry Gale about the balloon that brought him to the island. Sun decides whether to let Jin in on a secret.
When the hatch takes on a life of its own, Locke enlists the help of an unlikely ally. Ana Lucia, Sayid and Charlie seek the truth about Henry Gale.
Libby offers support to Hurley, who grapples with the past and the present when he spots an old friend on the island.
Rose pushes back against Bernard's plan. Sparks reignite between Jack and Kate as they propose a trade with The Others.
After finding an exhausted Michael in the forest, Jack and Kate bring him back to camp, where he shares what he learned about The Others.
Mr. Eko dreams about his brother leading him somewhere and asks for Locke's help finding it. Jack grapples with a situation in the hatch.
Michael convinces Jack to help him rescue Walt. Locke puts the survivors in danger while deciding if he should push the button.
After discovering something odd offshore, Jack and Sayid hatch a plan to confront The Others to get Walt back. Eko and Locke come to blows.
The survivors approach The Others by land and by sea. Years earlier, Desmond navigates a fraught relationship with his daughter.
Jack, Kate and Sawyer learn that The Others are more sophisticated and savvy than anyone guessed.
Sun's and Jin's lives are in danger as Sayid tries to locate the other castaways and capture The Others' attention.
Locke, Eko and Desmond are scattered after the hatch's implosion. Locke gets a message from the island.
The Others keep Sawyer and Kate in check. Jack is asked to use his medical training to save a life.
Eko wrestles with his reality, while other castaways go to the Pearl Station to locate Jack, Kate and Sawyer.
Pickett decides to make good on his threat. Locke discovers a hidden message that may unlock the island's secrets.
Ben's fate is in Jack's hands. Kate and Sawyer help Alex in return for a boat, and Juliet makes a bold decision.
After Desmond rescues Claire from drowning, Charlie gets Hurley to help him find out why Desmond can predict the future.
A power struggle ensues while Juliet's future hangs in the balance. Kate and Sawyer deal with the consequences of their escapade.
Kate struggles over the decision to leave Jack, while Hurley attempts to bring hope to a fellow survivor.
On a rescue mission, the survivors stumble upon a mysterious structure surrounded by farm animals and meet its strange proprietor.
Claire shares an idea to send a message to the outside world, but Charlie and Desmond are skeptical about its efficacy.
When Locke and Kate arrive at The Others' camp, Ben promises to tell Locke about the island's secrets — for a price.
The castaways try to figure out what happened to Paulo and Nikki, whose contentious relationship led them to the island.
The Others prepare to leave with a castaway in tow. Kate wakes up and becomes determined to get Jack.
Jack receives a cold reception upon his return. Juliet flashes back to her life before the island.
Desmond convinces Hurley, Jin and Charlie to follow him into the jungle. Years earlier, Desmond spends time with monks.
Sun learns what happens to pregnant people on the island. Juliet takes her to The Others' medical facility to learn the baby's date of conception.
Locke helps Sawyer eliminate a common enemy. At the beach, parachutist Naomi brings crucial information about Flight 815.
Locke confronts Ben and demands to be taken to Jacob. Ben remembers his childhood on the island and the early days of the Dharma Initiative.
Desmond foresees Charlie's death, but this time Charlie faces it head-on. Jack devises a plan to fight back.
The survivors prepare to defend themselves from The Others. Ben sends Mikhail to deal with Charlie at the Looking Glass.
Ben confronts Jack, claiming that Naomi is not who she seems. Inside the Looking Glass, Charlie and Desmond try to shut off the blocking signal.
The survivors think a rescue team is close, but they struggle to believe Charlie's final warning.
Hurley lets it slip that he saw Jacob's shack. Locke reveals who is giving his orders. Jack and Kate go to find one of The Others.
Sayid goes with Kate and Miles to the barracks to make a deal with Locke. In the future, Sayid is in Berlin with a killer new job.
Kate takes matters into her own hands to get information out of the hostage, only to cause problems with the camp's new leader.
On the way to the freighter, the survivors hit some turbulence. Jack wonders why Desmond thinks it's 1996.
Juliet gets a surprising visit from an old acquaintance, who orders her to stop Charlotte and Faraday.
Juliet reveals startling news to Jin when Sun decides to move to Locke's camp. On the freighter, Sayid and Desmond meet the ship's captain.
Sayid confronts Michael about his past. Back at camp, Ben sends Alex to a safer place.
When a body washes up on shore, Faraday tries to figure out what happened. Locke's camp receives an ominous warning.
Kate and Juliet must work together when Jack falls ill. Something goes wrong as Sawyer, Claire, Aaron and Miles trek away from Locke's camp.
While looking for the cabin, Locke, Hurley and Ben meet Christian, who is speaking on Jacob's behalf.
In the future, Jack, Kate, Sayid, Sun and Hurley reunite with loved ones. At a press conference, they lie about what happened on the island.
Ben tries to escape so he and Locke can fulfill Jacob's request. Michael tries to prevent catastrophe on the boat.
As the survivors face the mercenaries, the Oceanic Six find themselves closer to rescue.
Two of the Oceanic Six survivors come to grips with their need to return to the island — on their own terms.
The cops hunt down Hurley and Sayid. Jack and Ben try to bring everyone together, while Kate tries to hide the truth.
Desmond searches for a mysterious woman who can stop the island's time movements. Locke uncovers the person responsible for attacking the victims.
Kate discovers that someone knows the secret of Aaron's parental lineage. Time shifts place the remaining survivors' lives in peril.
Locke takes on the burden of stopping the increasingly violent time shifts. Ben hits a roadblock in bringing the Oceanic Six back to the island.
The way back to the island becomes clear to the Oceanic Six, but there's trouble ahead when not all of them wish to return.
Off the island, Locke assumes the pseudonym Jeremy Bentham.
Sawyer perpetuates a lie to protect the remaining survivors from the mistakes of their past.
When old friends return to the island, Sawyer must continue lying to protect them.
The survivors are at risk when one goes rogue and decides to take matters into his own hands.
Kate, Sawyer and Juliet try to save Ben. Kate starts to tell the truth to protect Aaron from harm.
To atone for sins of the past, Ben must attempt to summon the smoke monster in order to be judged.
Suspicions about a breach intensify after Ben is taken from the infirmary, and a reluctant Miles works with Hurley to deliver an important package.
A reckoning begins when Daniel Faraday comes clean regarding what he knows about the island.
Jack and Kate are at odds over how to save their fellow survivors, while Locke further solidifies his position as leader.
When Jack decides to set things right on the island, he's met with strong resistance from those close to him.
At the statue's remains, Locke assigns Ben a difficult task that could change Jacob's fate. Jack is determined to execute the plan.
The hydrogen bomb's fallout divides the group in more ways than one. Ben takes drastic action and makes an eye-opening discovery.
Those on the island face the aftermath of the explosion. The Man in Black's motives and the reason for his startling reappearance become clearer.
Jack continues butting heads with Dogen. Kate connects with Claire in the alternate timeline.
Sawyer follows the Man in Black, despite Richard's warnings. In Los Angeles, the survivors continue crossing paths in surprising ways.
With the help of an unexpected guide, Hurley leads Jack to a curious discovery. Jin has an encounter with an old friend.
The Man in Black continues appealing to different survivors. Claire sends a warning to those gathered at the temple about a coming danger.
On the island, Ben deals with the consequences of an uncovered lie. In a different reality, he schemes to advance in his teaching career.
Sawyer goes on a recon mission to the other island and has a run-in with another passenger from the flight in Los Angeles.
As Richard faces a difficult decision, clues surface about his history on the island and his relationship with Jacob.
Sun and Jin continue to search for each other on the island, while a customs seizure at LAX puts Jin in a difficult position.
Desmond wakes up in regrettably familiar surroundings and takes a trip between realities.
Hurley agonizes over the group's next move. Locke is curious about the new arrival, and the alternate story of how their paths’ cross unfolds.
A merger of the groups on the island immediately goes south, but the survivors have a promising backup plan.
When asked to perform a difficult task, Jack must decide whether or not to trust Locke. In another reality they meet under different circumstances.
The Man in Black's unsettling origin story finally explains Locke's intentions and his connection to the island.
A final showdown occurs on the island. Jacob appears to the survivors and agrees to answer their questions.
The survivors' stories come full circle on and off the island. Locke tests his tie to the island. A bittersweet reunion brings a final twist of fate.