The Grey Zone was a district of New Port City. It was populated by Gornt citizens of a lower social class than in the Black Zone. Access between zones was forbidden in order to prevent hate, pollution, and terrorism. The only way for Grey Zone inhabitants to move to the Black Zone was to win the lottery.
The Grey Zone had a mall and a pizza parlour. Iz was an inhabitant of the Grey Zone who gained access to the Black Zone. Her death led to an investigation by the Thirteenth Doctor and her companions. (PROSE: Gatecrashers)