Assassin's Creed: Brotherhood - The Da Vinci Disappearance

Meeting Leonard Da Vinci

*Mild Spoilers!* It is interesting that if the player decides to play the DLC alongside the main story he will eventually meet two versions of Leonardo Da Vinci. The first Leonardo will show up in the main game and offer his help and some quests. The second Leonardo is the one who's been captured by the mysterious cult. So it is absolutely possible to be playing the DLC quest of searching for Leonardo while chatting with the other Leonardo sitting on a bench in Rome. Talk about parallel worlds!