Mirage is set in Baghdad between 870 and 860 BC, after the anarchy of Samarra. The story revolves around a young Assassin named Basim Ibn Ishaq, initially a thief who joins the Hidden Ones, inspired by the Prince of Persia.
Here's the game's official synopsis: "In Assassin's Creed Mirage, you'll play as Basim, a skilled pickpocket with nightmarish visions, in search of answers and justice. You'll join the ranks of an ancient society and discover a new creed that will change Basim's fate in ways he never imagined."