Based on this trailer, season five will pick up directly where season four left off. Jack finds out that some very bad things happened after he left the island and Locke said he needed to go back. Ben tells him the only way to return is with everyone else who was rescued. The real question is, what kind of "very bad things" happened after Jack left? Where did the island go?What must they do when they return to the island? How did Locke bite the dust? With the faith vs. science debate that has made up Jack and Locke's bitter relationship throughout the series may be telling in Locke's death? Is it Jack and science, not Locke and faith, who should truly rule the island?
Now that the series finale has been determined, creators Damon Lindelof and Carlton Cuse now know where everything is going, so these final two seasons will be more directed, and hopefully brilliant. That is, combining the character study of season one with the mythology of season three and hopefully avoiding some of the clunkiness that made up season two.
Here's the moment you've all been waiting for: