Thief: Deadly Shadows is a stealth video game developed by Ion Storm for Microsoft Windows and Xbox that was released in 2004, on May 25 in North America and on June 11 in Europe.

It is set in a fantasy world resembling a cross between the Late Middle Ages and the Victorian era, with more advanced steampunk technologies interspersed.

Thief: Deadly Shadows received generally positive reviews, albeit not as critically successful as its predecessors.

The player takes the role of Garrett, an independent master thief who aims to steal his way through the City, using stealth, devices and weapons, in order to complete objectives and make profits on the side.

[4] Mission levels may be traversed by sneaking through the shadows, since walking or running will alert nearby guards, who detecting the presence of a vandal will search around for an unknown face.

Due to limited memory, city and mission levels are divided into parts connected by load zones.

Within the City, the player may sell previously stolen goods on the black market to fences, for gold, which can be used at various shops to purchase weapons, equipment and supplies.

As they are collected, loot, gold, equipment and weapons are retained in the player's inventory through the game, making it possible to 'hoard' for later use.

While exploring the City, the player may break into homes for additional loot, spy on and steal from the townspeople, and complete the occasional side quest.

Allying with major factions will motivate its members to fight alongside the player, against the City Watch guards.

Both the PC and Xbox versions of the game are relatively easy to play, with conventional and reconfigurable shooter-style controls.

After learning of a coming "Dark Age", Garrett steals an ancient book, the Compendium of Reproach, that details more about the event, along with a third Artifact called the Kurshok Crown.

Garrett suspects that the prophecy might refer to the city's clocktower, rather than time itself, and sabotages the clock, inadvertently causing the tower to collapse.

He discovers that the five Keeper Artifacts must be placed in specific locations around the City to activate the Final Glyph, which Gamall intends to destroy.

[10] According to Smith, the game was planned to take place in an "open-ended, self-directed city", and its plot was intended to focus on the Keepers.

[14] Ion Storm began by gathering a core team to design and plot the game, composed in part of ex-Looking Glass employees.

[15][16] Four key members of the Thief II team—Randy Smith, Emil Pagliarulo, Lulu Lamer and Terri Brosius—were hired to begin the project.

[17] Smith, the project leader, stated in December that pre-production was "going well", and he noted that Ion Storm was developing an early test demo.

[20] Visiting Ion Storm in May 2001, Chuck Osborn of PC Gamer US reported that Thief III had "just barely" started production.

The game is powered by a heavily modified and tweaked version of Unreal Engine 2, which Ion Storm had previously used in Deus Ex: Invisible War.

Ion Storm decided not to call the game Thief III for fear that it would alienate those who had never played the previous two titles.