Secret Masks are a type of collectible in Sly Cooper: Age of Thieves.
Unlike in Sly Cooper: Thieves in Time, which had only Secret Sly Masks that could give any of the four main character (Sly, Murray, Bentley, and Carmelita) skins, there are now four more Secret Masks in the sequel: Secret Bentley Masks, Secret Penelope Masks, Secret Murray Masks, and Secret Carmelita Masks. These masks fill the same purpose as the Secret Sly Masks, but they are, like the Secret Sly Masks in Age of Thieves, more specific, only giving additional skins to the specific characters that the masks represent. In levels, they normally stay in the same spot. However, in hubs, they will be randomly placed, making them much harder to find. Collecting masks will add to the overall completion of the game.