Because You Left is the first episode of season 5 of Lost coming Wednesday January 21st, 2009 at 8PM EST on ABC. Click the title link for a sneak peek.
If you haven't watched Lost, or are not caught up to season 5 yet... you can watch all the episodes for free online here. So what are you waiting for?! This is the best show ever ever ever times a million.
Further your Lost knowledge acquisition at Lostpedia.
You can catch up on seasons one through three in 8 minutes and 15 seconds here. This is the official recap, but beware, it's all spoilers!