Each half-hour episode is a self-contained story with new characters and a new setting, and all star at least one (usually both) of Pemberton and Shearsmith. Aside from the writers, each episode has a new cast, allowing Inside No. 9 to attract a number of well-known actors. The stories are linked only by the number 9 in some way and a brass hare statue that is in the background of all episodes. Settings have included a suburban house, a gothic mansion and a barn.
Pemberton and Shearsmith took inspiration for Inside No. 9 from an episode of Psychoville, a previous project, which was filmed in a single room. This episode was, in turn, inspired by Alfred Hitchcock's Rope. Inside No. 9 was also a reaction to Psychoville, which featured a long overarching story realised over multiple series.