You start in a prison cell. The first step is to interact with the bed to find a hidden item. After a brief cutscene, a guard will approach. Use the opportunity to perform a CQC takedown when he opens the door. Drag his body into your cell to hide it. Pick up his uniform and equip it to blend in. This is your first taste of disguise mechanics. Proceed cautiously out of the cell block, using the radar to monitor guard patrols. Avoid direct confrontation if possible, as you are currently unarmed.
