Michael convinces Jack, Kate, Sawyer and Hurley to help him rescue Walt. At the double funeral for Ana Lucia and Libby, Sayid tells Jack of his suspicion that Michael has been compromised by the Others. Flashbacks reveal Michael's time being held captive by the Others, during which he made a deal to first release Henry, and then trade Jack, Kate, Sawyer and Hurley for Walt. Sun spots a sailboat floating towards the beach.
(From Wikipedia)