Jack, Sawyer and Kate are all in various forms of captivity around a Dharma station called the Hydra. Jack is quizzed by Juliet and when he attacks her and escapes he discovers he is being held under water. Sawyer is in a polar bear cage and is helped to escape by a young man. He is soon back in his cage and works out how to get food from devices in the cage. Kate is given an elegant breakfast with Ben (Henry Gale) who tells her the next two weeks will be unpleasant.

Sayid brings the boat ashore to start another signal fire. Jin wants to leave but Sun lies to him in order to help Jack. Sayid plans to ambush the Others and Jin works out what is going on. He tells Sun to wait in the boat. She ends up shooting one of the Others when they take the boat. She escapes though and Sayid apologises to them both as they head home. Sawyer and Kate are put to work by the Others. Jack is shown footage of Boston winning the World Series by Ben who tells him that if he cooperates he can go home.

Locke wakes up in the jungle but can’t speak. He builds a sweat lodge where “Boone” tells him to save Eko from a polar bear. Charlie joins Locke and they encounter Hurley who in turn meets a naked Desmond. Locke saves Eko and tells the survivors that he will save Jack from the Others.

Desmond builds a lightning rod outside Claire’s tent and catches a bolt which might have hit her roof. The Others ask Jack to help with the dying Colleen. He can’t save her but does see some spinal x-rays. The Others put a pacemaker in Sawyer and tell him his heart will explode if he doesn’t behave. Eventually Ben takes Sawyer up a cliff to show him that they aren’t on the same island anymore, so there is no where to run.

Eko staggers through the jungle in search of Yemi. Locke leads a group to the pearl station. Once there they use the a feed to see into another station and see a one-eyed man. Eko gives “Yemi” his confession before the smoke monster appears and kills him. Meanwhile Jack realises that it is Ben who has the tumour. Ben asks Jack to do the surgery while Juliet suggests that he let Ben die.

Locke buries Eko with his Jesus stick and sees a message on it. The Others tell Kate to convince Jack to perform surgery or they will kill Sawyer. Kate and Sawyer sleep together and when Jack sees them he agrees to do the surgery. During it he threatens to kill Ben unless Kate and Sawyer are allowed to escape.

Alex offers to help Sawyer and Kate if they take Karl with them. They free his from a room where he is being brainwashed and put him in a boat. Juliet kills Danny in order to let them go. Jack finishes the surgery and asks Juliet what Ben said to her in order to get her to help. She says she has been on the island for three years and now he will let her go home.

Desmond runs into the sea to save Claire from drowning. Charlie and Hurley get Desmond drunk in order to find out how he seems to know the future. Desmond admits that when he turned the fail safe key his life flashed before his eyes. And now he is still seeing those flashes and they are of Charlie dying.

Jack agrees to help Ben recover in exchange for Juliet’s life. She avoids execution and the Others take Jack back to the main island. Kate and Sawyer head back to camp leaving Karl to go in search of Alex. in

Hurley finds a Dharma van and is determined to get it started. Charlie, Sawyer and Jin help him out. Kate rushes off to find Rousseau in order to track Jack down.

Following Eko’s compass bearing, Sayid, Locke, Kate and Danielle find a Dharma station called The Flame. It is a communications station and they find the one-eyed man inside who tells them he is the last remaining member of the Dharma Initiative. Sayid realises he is lying and they capture him and find Miss Klugh in the basement. Locke finds a computer which allows him access to emergency instructions from Dr Marvin Candle. Mikhail shoots Klugh but Sayid refuses to kill him. Locke enters 77 into the computer and the station soon explodes. On the beach the survivors rebuild the table tennis table from the Swann. Sawyer wants his stuff back so he plays Hurley to get it back. But when he loses he is forced not to use any nicknames for a week.

Claire sees migrating birds and thinks she can attach a message to a tagged bird to help find rescue. Desmond and Charlie try to dissuade her and have secret conversations. Eventually she follows Desmond who captures a bird for her and tells her the truth about his visions. Sayid and company find a defence system around the Others camp and Locke kills Mikhail by throwing him through the sonic barrier. They climb over it and arrive at the Others camp only to find Jack playing football with Tom.

Kate and Sayid are captured trying to talk to Jack. He tells her that once he is off the island he will bring rescue. Locke heads to Ben’s house and admits he is going to blow up the submarine. Ben lets him blow it up and admits that it allowed him to keep Jack and Juliet on the island. He then shows him Anthony Cooper who he claims came to the island from a magic box.

Nikki stumbles out of the jungle and falls down dead in front of Sawyer and Hurley. They find Paulo dead too in the jungle. They find one of the Others’ walkie-talkie’s in their possessions and some diamonds buried near Paulo’s body. Suspicion falls on the monster and then on Sawyer. Charlie admits to Sun what he and Sawyer did to her (in 213). The camp bury Nikki and Paulo alive.

Locke says goodbye to Kate and leaves with the Others. She gets gassed and wakes up in the jungle handcuffed to Juliet. They walk back to the barracks and avoid the smoke monster. Juliet is forced to admit that she handcuffed them together so that Kate would sympathise with her for being left behind too. They return for Sayid and Jack and Jack insists that Juliet return to the beach with them. Meanwhile at the beach, Hurley tells Sawyer that he needs to treat people better or they will banish him from the camp.

Sayid leads Kate, Jack and Juliet back to the beach where Claire is ill. Juliet says she can make Claire better because she is reacting badly to the injections Ethan gave her. When Claire recovers the survivors allow Juliet to live in their camp.

Desmond has a flash of Charlie dying and someone coming to the island with his photo of Penny. He recruits Hurley, Jin and Charlie to come camping with him. Once out there a helicopter crashes into the ocean and a beacon flashes above the jungle. Desmond prevents Charlie from dying but is scared he has changed the future. When they find the woman who bailed out, it isn’t Penny but she recognises Desmond. Meanwhile Kate is upset to see Jack spending time with Juliet and so she seeks comfort from Sawyer.

Sun becomes suspicious after Jack asks her questions about her pregnancy. When Kate tells her that Juliet was a fertility doctor she demands to know what happens to pregnant women on the island. Juliet takes her to the medical station to perform an ultrasound. Sun confesses that the baby may not be Jin’s. It turns out that it is but that means Sun will die. Meanwhile Hurley accidentally sets off a flare attracting the attention of Mikhail. He helps fix the parachutist’s wounds in exchange for his freedom. She claims that Flight 815 was found with all the passengers dead.

Locke comes to see Sawyer and tells him he has Ben tied up and wants him to kill him. He tells Sawyer that he read his file and he knows about the man he killed and that’s why he came to him. Once at the Black Rock it turns out to be Anthony Cooper tied up and not Ben. Locke locks Sawyer in with him. Sawyer soon realises that Cooper is the original Sawyer and he strangles him. On the beach Hurley and company confide in Sayid about Naomi the parachutist. Kate discovers what’s going on and tells Jack.

Locke arrives at the Others’ camp with his father’s dead body. He demands that Ben take him to see Jacob. Ben takes him there and though Locke can’t see Jacob he hears him. Ben takes Locke to the mass grave of the Dharma Initiative, shoots him and leaves him there. At the beach Sawyer plays Juliet’s recording to Sayid and he informs the whole camp just as Jack and Juliet return with a plan.

Desmond tells Charlie that he sees him drowning in order for Claire to be rescued. It seems that his destiny when Jack and Sayid discover Ben is blocking all signals from the island using an underwater station. Charlie volunteers to deactivate it and begins writing a list of the best moments of his life for Claire. Karl arrives to alert the survivors that the Others are coming a day early. Sayid convinces Jack to head to the Radio Tower with the other survivors (to switch off Rousseau’s signal) while he stays behind with Bernard and Jin to shoot the dynamite.

Jack leads the survivors to the radio tower. Sayid, Jin and Bernard stay behind and fail to kill all of the Others who come to their camp. Down in the Looking Glass station Charlie tells the women the truth about why he is there. They are soon joined by Desmond and Mikhail. Once he hears all the news, Ben takes Alex with him to try and persuade Jack not to leave the island. Locke tries to kill himself but Walt intervenes.

Ben confronts Jack but doesn’t convince him not to leave the island. Charlie turns off the jamming equipment and makes contact with Penny. Just as he does Mikhail floods the station and Charlie chooses to die to protect Desmond. Hurley uses his van to attack the Others and Sawyer kills Tom, despite his surrender. Alex and Danielle are reunited. Naomi contacts her boat but is killed by Locke who can’t bring himself to kill Jack. Jack makes contact with the boat.