The first part of the season finale begins with a warning from the mysterious French woman.
“The Others are coming,” declares Rousseau. “You have only three choices: run, hide, or die.”
At this point we know absolutely nothing about “the others” other than they apparently stole Rousseau’s baby sixteen years ago. But the survivors of 815 decide to air on the side of caution and go with the “hide” approach. The plan: follow Rousseau to the Black Rock to get some dynamite, blow open the hatch, and hide everyone inside.
So Jack, Kate, Locke, Hurley, Arzt and Rousseau venture out to find the dynamite while Michael, Walt, Jin and Sawyer set out to sea on the raft.
Random Side Notes:
Walt gives Shannon custody of Vincent while he leaves on the raft.
Jin and Sun reconcile, but Jin still leaves on the raft because he says it’s his duty to save Sun.
Before the raft leaves, Sawyer tells Jack about the conversation he had with Christian in Sydney (how he said he knew their falling out was his fault and that he’s very proud of Jack). This is probably one of the most touching moments in Lost history.