Season 5 of lost is about to start. Catch up on what's happened so far.

Recap
Oceanin Flight 815 crashes on an island.
Jack becomes the leader and likes Kate.
Kate is a fugitive and likes Sawyer.
Locke was in a wheelchair, but can now walk.
Hurley won millions in a lottery.
Claire is pregnant with her son Aaron.
The Others live somewhere else on the island, and are lead by the evil, Henry Gale, real name Ben.
Locke finds a hatch that is eventually opened.
Desmond lives in a bunker.
Henry takes some passengers prisoner.
Jack and Locke fight.
In the future, Jack and Kate have escaped the island. Jack said they had to go back, so they're back on the island in the present.
A ship arrives.
Desmond travels through time.
Ben and Locke move the island.
The ship explodes.

What lies ahead
In the first episode, the big secret explaining what the show is all about is finally revealed - but this also creates new mysteries and more questions. It's all about time and time travel. Everyone (or let's call them the six who escaped) will be back from the future where the fourth season ended, because they heeded the mysterious phone call to Kate - a message that, played backwards, said, "The island needs you. You have to go back before it's too late".

Time facts to keep in mind
Watch the scene where Ben crawls down the ice cavern and turns the wheel again - it will explain season five's opening sequence.
Keep a constant look out for all the items that Locke touches.
In season four, Ms Hawkings told Desmond time couldn't really be altered.
Island time travellers tend to get sick, have nose bleeds and die.
Sickness can be slowed or cured by fixing one's mind on a source of meaning.