During a routine trip from Sydney, Australia to Los Angeles, Oceanic Flight 815 is blown off course and crashes on a remote Island. Thinking that rescue will soon be coming, the survivors tend to the injured on the beach and set up camp. Jack, Kate and Charlie hike through the jungle to retrieve a transceiver from the cockpit, but are attacked by the "Monster".
Jack, Charlie and Kate return to the beach camp with the transceiver. Sayid, a former military communications officer, gets the transceiver working but tells the others he can get better reception if they head to higher ground. When they get there, they pick up a mysterious distress signal in French that has been playing on loop for 16 years. The group is attacked by a polar bear, and learns that there was a convict on the plane.
Jack discovers that the injured man he has been trying to save is a U.S. Marshal, and learns that Kate is the convict. Meanwhile, single father Michael questions his son Walt about a conversation he had with another passenger, John Locke.
Locke, a wheelchair-bound cubicle worker, is denied access to a walkabout.
After a group of boars raid the fuselage in the middle of the night, Jack decides the bodies need to be disposed of. As the survivors' food supply runs low, Locke leads a boar hunt and encounters the Monster. Claire and Sayid organize a funeral service.
While bordering on exhaustion, Jack repeatedly sees a mysterious man watching him from afar, but no one else can see him. Haunted by the strange vision, Jack follows the man, only to recognize him as someone to whom he was very close. Meanwhile, the water supply runs dangerously low, a situation that erupts in violence when someone steals the last remaining bottles. Jack returns to the beach, having found fresh water in the nearby caves.
Sun contemplates leaving Jin and starting a new life.
Jin, a Korean castaway who speaks no English, assaults Michael, seemingly without provocation. Sayid resolves the conflict by handcuffing him to the wreckage. Jack's decision to move to the caves causes division among the survivors. Sun must decide whether or not to free her husband, at the cost of a long-hidden secret.
Charlie goes through a personal crisis and becomes addicted to heroin.
Charlie goes into withdrawal when Locke takes his remaining bags of heroin. Jack becomes trapped in a cave-in. Sayid tries to triangulate the French woman's signal, but his efforts are thwarted by a mysterious attack.
Sawyer struggles with his personal demons as he attempts to con Jess.
The onset of an asthma attack threatens Shannon's life, and the only man who can help her is Sawyer, whom Boone believes stole her inhalers from the fuselage. When Sawyer refues to help, Jack and Sayid must decide whether to resort to violence to retrieve the medicine. Meanwhile, Sayid attempts to learn who attacked him in the jungle.
Sayid reluctantly tortures Nadia during the Gulf War.
When a golf bag is found in the wreckage, Hurley constructs a golf course to give the survivors a much-needed recreational outlet. In the jungle, Sayid's attempt of exploring the Island ends when he falls into a trap set by a mysterious French woman named Danielle Rousseau. Sayid's overtures of friendship are rebuffed as Rousseau resorts to torture, believing him to be part of a mysterious tribe already living on the Island.
After learning she is pregnant, Claire must decide either to keep her baby, or put it up for adoption.
Claire is haunted by nightmarish visions that her baby is in danger, and later appears to be attacked, but no one believes her. Hurley suggests that they compile a list of the survivor's names and use the manifest as a reference. When Hurley compares the two, it leads to an unnerving conclusion about a passenger named Ethan Rom.
After the news about Hurley's census is discovered, Jack and Locke search for Claire, but discover that she, Charlie, and Ethan are missing. After joining the search for Claire, Boone and Locke make a discovery that will change the lives of everyone on the Island.
Enlisting Shannon to help translate the papers he stole from Rousseau, Sayid makes a startling discovery. Meanwhile, Kate and Sawyer find a briefcase in wreckage submerged in a hidden lagoon, and find themselves pitted against each other when it becomes clear that the contents of the case hold vital information about Kate's past.
Danielle kidnaps Claire's baby in hopes of making a trade with "the Others." Locke blows open the hatch as a possible shelter for the survivors. The raft party makes contact with a not-so-friendly boat crew.
Rousseau leads Sayid to a stranger she's caught in the jungle; Sayid uses torture to attempt to determine if he is an Other; Hurley and Sawyer search for a tree frog in the jungle.
Sun discovers she is pregnant; Ana Lucia is recruited to help interrogate Henry Gale. Ana Lucia, Charlie, and Sayid journey into the jungle to confirm if Gale's story is the truth
Bernard attempts to assemble an enormous SOS sign on the beach; Kate and Jack go into the jungle to propose a Henry Gale-for-Walt swap with the Others; Michael returns.
Eko and Locke find the Pearl Station; Michael must maintain his cool as he watches Libby die slowly; the rest of the survivors must cope with the situation.
Hurley begins to suspect that Sawyer may be involved in Nikki and Paulo's apparent death, and Sun learns the truth about her past kidnapping attempt by "The Others".
Ben's mother dies in childbirth. Years later, he and his father come to the island as DHARMA workmen.
Ben remembers arriving on the island with his father and growing up to become the leader of "The Others". Ben takes Locke to see Jacob. Meanwhile, Juliet's secret is exposed to the camp, as is Naomi.
Three years after the crash, Jack suffers from depression and drug/alcohol abuse.
Jack and the castaways begin their efforts to make contact with Naomi's rescue ship. Charlie is held captive in the Looking Glass. The ploy at the beach does not go as planned.
Feeling that their rescue is close at hand, the survivors don't know whether to believe Charlie’s final message that the people claiming to liberate them are not who they seem to be...
Locke's hostage may be the key to getting off the island, so Sayid and Kate go in search of their fellow castaway in an attempt to negotiate a peaceful deal.
Juliet receives an unwelcome visit from someone from her past and is given orders to track down Charlotte and Faraday in order to stop them from completing their mission. Meanwhile, Ben offers Locke an enticing deal.
Jin, in the past, is running an errand for Mr Paik. Sun, a member of the Oceanic Six in the future, gives birth to a girl.
Juliet is forced to reveal some startling news to Jin when Sun threatens to move to Locke’s camp. Meanwhile, Sayid and Desmond begin to get an idea of the freighter crew’s mission when they meet the ship’s captain.
Jack sees a vision of his father in the future, while his relationship with Kate begins to fall apart.
Juliet and Kate must work together to save Jack when his health is seriously compromised. Something goes wrong as Sawyer, Claire, Miles and Aaron head back to the beach.
Just after his rescue, Hurley does not completely agree with Jack's decision to lie.
In 2007, Hurley, who is on the run from the police with Sayid, has trouble dealing with the secret of the Oceanic 6. Meanwhile, Kate meets an old friend to get some advice. On the island, The remaining survivors continue to feel the effects caused by the Island being moved through time, and later come under attack by unknown forces.
In 2007, Desmond goes in search of a woman who could be the key in helping Faraday stop the Island's erractic movements through time. In 1954, Miles, Daniel, and Charlotte are taken captive by the Others while Sawyer and Juliet try to save them. Locke meets with Richard.
Just after her rescue, Kate decides to take custody of Aaron.
In 2007, Kate attempts to learn who is trying to obtain custody of Aaron, while Ben continues his quest to reunite the Oceanic 6. On the island, The dramatic shifts through time place the lives of the remaining Island survivors in extreme peril, forcing Locke to attempt to return to the Orchid in hopes of escaping the Island.
Sun confronts Ben over the death of Jin, and Ben hits a major roadblock in his attempt to reunite the Oceanic 6 and bring them back to the Island.
Locke takes on the burden to stop the Island's increasingly violent shifts through time. In 1988, Jin witnesses the downfall of the Science Expedition.
Miles, realizing he has the ability to communicate with the dead, is recruited by Naomi to join the crew of the Kahana.
A reluctant Miles is forced to work with Hurley when he's asked to deliver an important package to a top DHARMA official. Meanwhile, suspicions about a possible security breach intensify after young Ben is taken from the infirmary.
Jack and Kate find themselves at odds over the direction to take to save their fellow Island survivors, while Sawyer and Juliet come under scrutiny from the DHARMA Initiative.
Locke further solidifies his stance as leader of The Others, though worrying Richard and Ben about his true intentions.
Jacob sets his plan in motion by visiting many of the survivors at pivotal moments in their lives.
In 1977, Jack's decision to put a plan in action in order to set things right on the Island is met with some strong resistance by those close to him. In 2007, Locke assigns Ben a difficult task.
The battle lines are drawn as the Man in Black puts his plan into action, which could finally liberate him from the Island, while Jack and the remaining survivors take their final stand to save the Island from destruction.
