Full Synchronisation Requirement - Do not wander far from Yusuf
Simply follow Yusuf and listen to his explanation of the situation in Constantinople. Walking alongside him will have Ezio start to move automatically, saving you a little effort. Many little tooltip tutorials will appear on the screen during this Memory, so pay attention to learn a few useful tricks for later use.
Eventually you and Yusuf will be attacked by a small group of Byzantine Templar guards. Take them out using combos and executions. When confronted by the next group, they’ll be immediately chased off helpfully by the local Janissaries, the bodyguard of the Sultan and his family. After that confrontation, simply follow Yusuf the rest of the way to the Galata Assassin Den.