Thief: Deadly Shadows is a stealth-based game developed by Ion Storm Austin rather than Looking Glass Studios (albeit with many of the same people), and is a relative departure from the first two games in the series. The game is powered by the Unreal-based Deus Ex: Invisible War engine and unlike the original two titles, Deadly Shadows was developed simultaneously for Microsoft Windows and the Xbox.

You play Garrett: The Protagonist, Hero (or Anti-Hero, as many would argue), Master Thief, and Expert Assassin. Garrett is a solitary thief, who is willing to steal anything, and, if necessary, kill to get what he wants. Garrett is a simple man, with a rather large title, but who says it's easy being the greatest thief that ever lived? Pick locks, pickpocket people, mug people, scale buildings with ease (Requires Climbing Gloves; found in the shop in the Docks). Garrett's stealth knows few bounds, and he has became a legend amongst his own kind.

One of the game's major new features was the ability to explore the City. While previous games sent Garrett straight from mission to mission, Thief: Deadly Shadows allows him to walk the City streets between missions where he can steal from passersby, spy on the townspeople, and complete the occasional sidequest in addition to major story missions. Unlike games such as Grand Theft Auto III, the city is not one large continuous map, but rather several small neighbourhood maps connected by load zones.