Prologue - Animus Island
Waking up, you (as Desmond) find yourself on a beach, alone. When you gain control, move up the beach, taking in the scenery until you meet Subject 16.
Follow him up the slope towards the light, listening to his explanation of where you are and the task you have before you. As Subject 16 explains, your mind has become fragmented through the events of the previous games, and it’s up to you to delve deeper into the events of your ancestor Ezio Auditore’s life to allow the Animus to piece your consciousness back together and return your mind to your body.
The Animus Island serves as a hub connecting you to both the main game (Ezio’s memories) as well as the extra Desmond levels in which you explore the Animus itself in search of answers. These latter areas are unlocked when you obtain enough Animus Data Fragments in Constantinople as Ezio - but more on that later!
For now, when directed, head into the glowing gate of light in search of your 'synch nexus'.