The library holds not only hidden knowledge but also the most unsettling secret the world has ever known, a secret the Templars hope to use to control humankind's destiny. Five keys are needed to access the library-to find them, Ezio must travel to the troubled city of Constantinople, where a growing army of Templars threatens to destabilize the Ottoman Empire. Walking in the footsteps of his predecessor, Altaïr, Ezio must defeat the Templars for the final time. The stakes have never been higher, and what started as a pilgrimage has become a race against time.