If you want to avoid spoilers because you just started playing BioShock Infinite, you should probably stop reading now. If you are caught up or don't mind a few end details, then Irrational Games heads back to Rapture to continue Elizabeth's adventure.
The latest trailer for Burial at Sea: Episode 2 follows Elizabeth as she tries to rescue Sally from the ruins of Rapture. The preview clip prepares for the Episode 2 release scheduled for launch sometime before March 31. It's not the most accurate date, but the only timeframe available.
Burial at Sea and the rest of the BioShock Infinite DLC can be purchased part of the BioShock Infinite Season Pass. To mitigate the cost of full BioShock release, players can download Infinite free as part of January's PlayStation Plus Subscription.