Following Garrett's previous adventure, the repercussions of his actions have changed the political landscape. The Hammerite religion has crumbled and a new leader named Karras has risen up to convert many of these fanatics over to the mysterious Order of Mechanists. Meanwhile, a new Sheriff has arrived in town and has been effective at cleaning up crime - maybe too much so. This is bad news for Garrett, whose profession of master thief puts him on the wrong side of the law. As the risk increases however, so too does the amount of treasure available to a skilled thief.

Thief II: The Metal Age keeps much of the same gameplay and abilities from the original Thief: The Dark Project, but also offers a few new items for the protagonist to use. Among them are scouting orbs, which can be thrown to see around corners and flash mines. The heart of the gameplay is still stealth, made up of Garrett's ability to stay quiet, stay hidden and keep signs of trouble out of anyone's view. Garrett's main weapons are his sword, his blackjack and an assortment of arrows, each with a special power. Each level features a variety of objectives as well as several items which don't belong to the protagonist, but are nonetheless valuable and can be stolen.