Details and a trailer for the next Assassin's Creed: Revelations DLC, "The Lost Archive", was leaked via retail Zavvi earlier today. The DLC will be available on Xbox Live and PSN on February 28th.
"The Lost Archive" features a series of narrated first-person puzzles similar to Desmond's memory segments where Clay Kaczmarek, A.K.A. Subject 16, tells the story of how he got lost in the Animus.
On top of the story missions, "The lost archive" gives players three multiplayer character skins and three sets of special armor: Ezio's Turkish Assassin Armor, AltaĂŻr's robe and the Armor of Brutus.
At this point there's no way to tell whether or not "The Lost Archive" serves as a lead-up to the third Assassin's Creed, though the extra back-story may make this a must-buy for fans interested in the series' larger universe.