The season 3 finale finds the castaways preparing for an invasion by the slightly less mysterious Others, while Charlie and Desmond find more than they were looking for in the underwater "Looking Glass Hatch".

The season 3 finale finds the castaways preparing for an invasion by the slightly less mysterious Others, while Charlie and Desmond find more than they were looking for in the underwater "Looking Glass Hatch".

Ben unwillingly divulges information to Locke about the island, taking him on a journey to various locations including strange monuments and the mysterious Jacob. Back at the beach, Juliet's secret is revealed. Flashbacks will show us the origins of DHARMA and the history of the island, including 'the purge.'

After Desmond rescues Claire from drowning, Charlie gets Hurley to help him find out why Desmond has seemed able to predict the future. Desmond recalls exactly what took place in the moments after he turns the key, where he experienced a strange vision of his life prior to his Army days.

When Kate and Locke arrive at the Others' camp, Ben promises to tell Locke the island's secrets as long as he stops his destructive plan, and Kate's reunion with Jack doesn't go very well when she learns that the Others have offered him a deal. More of Locke's troubled past is revealed.

While Jack devises a plan to do away with "The Others" once and for all, Sayid uncovers a flaw in "The Others'" system that could lead to everyone's rescue. But it requires Charlie to take on a dangerous task that may make Desmond's premonition come true. A Charlie-centric episode.

After abandoning the Others, Locke takes Sawyer on a trek through the jungle to help him eliminate a common enemy. Meanwhile, back at the beach, the parachutist Naomi has crucial information about flight 815.

Jack has the Others in a desperate situation as he holds Ben's life in his hands. Meanwhile, Kate and Sawyer try to escape from their captors. Flashbacks reveal Juliet's past as a medical researcher in Miami.

The celebration of Jack's return is cut short when he arrives at the beach with an Other, Juliet, whose flashbacks pick up from where they left off, showing us how she got onto the island and became an other. Meanwhile, Claire is threatened by a strange illness.

Jack, Kate, and Sawyer are prisoners of the mysterious "Others." After their captors drug them and take blood samples, they are held in separate areas. The camp leaders--Ben (Henry Gale), Mr. Friendly and a new woman, Juliet--try to make the castaways adjust to their new circumstances. Flashbacks reveal more about Jack's past with his father and his wife Sarah.

Jack makes a decision regarding Ben's offer. Sawyer's life is placed in danger when Pickett decides to make good on his threat. Locke discovers a hidden message that may help unlock the island's secrets. Kate recalls memories from the past, which caused her to make an important choice.

On their mission to rescue Jack, Kate, Sayid, and Locke stumble upon a mysterious structure surrounded by farm animals and meet its strange inhabitant. Back at the camp, in order to reclaim his belongings, Sawyer plays in a ping-pong competition.

Desmond convinces Hurley, Jin, and Charlie to follow him on a trek through the jungle after he receives a series of visions. Flashbacks reveal the time that Desmond spent with a cloister of monks. Meanwhile, a despondent Kate turns to Sawyer for companionship after seeing Jack and Juliet together.

The Others prevent Sawyer and Kate from escaping, leaving Sawyer perplexed by the extent of the measures taken to keep them imprisoned. Jack is asked to use his medical training to save the life of one of the Others. At the beach, Desmond's strange behavior attracts attention. He begins to construct a mysterious device.

Kate is still struggling over their decision to leave Jack in the hands of the Others as she and Sawyer return to their camp. Meanwhile, Hurley finds an old van in the jungle and attempts to use it to help a fellow survivor in need of faith and hope. Flashbacks reveal more of Hurley's tumultuous past with the numbers curse.

Claire has an idea to send a message to the outside world. Charlie, however, is resistant to the idea, and Desmond tries to sabotage the plan. As Claire tries to get the truth behind their actions out of the pair, she remembers traumatic events from her past. Meanwhile, the rescue party encounters a dangerous obstacle.

Sun allows Juliet to examine her when she learns that all of "The Others" pregnant woman died before they gave birth on the island. Meanwhile, Desmond and an unlikely nemesis collaborate to save a new island inhabitant's life.

A delirious Eko wrestles with past demons; some of the castaways go to the Pearl station to find a computer they can use to locate Jack, Kate and Sawyer; Jack does not know who to trust when two of the Others are at odds with each other.

Kate and Juliet are stranded in the jungle after Kate learns that there is a traitor in the survivor's midst. Meanwhile, Sawyer's poor attitude and selfish ways towards the beach community may earn him a vote of banishment if he doesn't have a change of heart.

Sun and Jin's lives are put in danger when Sayid tries to locate Jack and the other missing castaways. Sayid also creates a plan in order to get the attention of the "Others" on the beach. Meanwhile, Henry (i.e. Ben) gives Jack an offer that is very tempting in exchange for his cooperation. Lastly, Kate and Sawyer must adjust to harsh conditions that are being forced upon them by "The Others."

As the truth about Sun's kidnapping by "the Others" comes to her attention, Hurley becomes suspicious of Sawyer's attempt to reveal the mystery behind two fellow survivors, Nikki and Paulo. Through series of flashbacks we will discover what Nikki and Paulo were doing before the crash and how they survived 65 days on the island.

Locke, Eko and Desmond are found scattered about the island after the implosion of the hatch. Locke receives a message from the Island asking him to fix the situation he caused. Hurley returns to the beach camp to report the imprisonment of Kate, Jack and Sawyer by the Others. Desmond has been fundamentally altered by the implosion, giving him a mysterious new power.

As Kate and Sawyer journey back to the main island with Karl, who is exhibiting effects of the brainwashing video, they argue over whether to go back and save Jack. On Hydra island, as Juliet's fate rests in his hands and a power struggle within the Others ensues, Jack recollects the time he spent in Phuket, Thailand and his relationship with Achara, a mysterious tattoo artist.