Ankh-Morpork is a city surrounded by darkness, where the cold river Ankh flows, where it always rains, and where dwarves and trolls co-exist with secret societies, religious fanatics, stupid police captains, and bar pianists. It is also where a bitterly sarcastic sharp-eyed private investigator named Lewton tries to earn a living solving bizarre cases. A mysterious woman named Carlotta hires him to find her lost lover. Wandering through the dark city and gathering evidence, Lewton has to solve the case, confront a sinister conspiracy, and once again become torn between love and despair.

Discworld Noir differs from other Discworld adventure games not only thanks to its more serious tone and much darker "film noir" atmosphere, but also because of its gameplay. Instead of inventory-based puzzles there are clues, which Lewton writes down in his notebook and which should be then used whenever there is a connection between the clue and the situation in question. Most of the gameplay is thus dedicated to detective work in conversations; but the usage of the right clues at the right place is still comparable to inventory-based puzzle-solving of other adventures. Graphically, Discword Noir features three-dimensional character models and pre-rendered backgrounds.