Assassin's Creed Revelations Walkthrough Part 1 – The Hangman

After a nice little recap of events, with minimal spoilers, Desmond comes to inside the Animus's Safe Mode. He is only partly aware of the events happening around him. Run forward for the next cut-scene where you will encounter Subject 16 who explains something of you present situation. He explains that you need to reach a Synch Nexus. This process has you completing unfinished memories of both Ezio and Altair. You regain control in front of the portal into the deeper memories. Hold up a moment to listen to the dialogue between everyone on the outside.

With that completed, head forward into the portal. Keep moving even when the screen is white. There is a little more distance than just walking through it. There is a cutscene for the introduction to the game that finishes out the sequence shown so many times in the trailers.