The show was set in Room 17 of the Department of Social Research, where former wartime agent-turned-criminologist Edwin Oldenshaw (Richard Vernon) solved difficult police cases through theory and discussions with his assistant (originally Ian Dimmock (Michael Aldridge), later succeeded by Imlac Defraits (Denholm Elliott), owing to Aldridge becoming ill).

In the last episode, Oldenshaw and Defraits are in a park, feeding waterfowl, and the camera zooms in on their briefcases, bearing their initials: E.G.O.

The novelty of the series was that Oldenshaw and his colleagues never needed to leave their office in order to resolve cases, preferring to spend their time playing the board game of Go.

Different directors were often appointed to film the Room 17 and outside-world scenes independently, to maintain a sense of distance between the two worlds.

The rarefied nature of Oldenshaw's work was amplified in 1967 when he returned, re-united with Dimmock, in a new series, The Fellows (Late of Room 17).