The Dark Project (some spoilers)
Thief: The Dark Project reveals the origins of Garrett's amazing thieving abilities. Taken in as a young child by a secretive group called the Keepers, Garrett was trained to go silent and unnoticed through the city. Garrett, however, rejected the Keepers' ideas about protecting the city silently. He left them to pursue his own path - that of the thief. Garrett's luck has been on the slide when a mysterious woman named Viktoria appears on his doorstep with an interesting proposition. Her associate, a wealthy nobleman named Constantine, wished to hire Garrett to "appropriate" a mystical artifact called the Eye. Despite the fact that the Eye has been locked away behind magical barriers by the Keepers and requires four other artifacts to unlock it, Garrett's pride won't let him back down until the job is done. But is he prepared for the consequences?
The Dark Project was later rereleased as Thief Gold, and contained three new missions and integrated previous patches.