London in the 1920s. Sitting in the corner of a branch of the (long defunct) ABC Tea Rooms sits a shabbily dressed old man, who looks more like a tramp. He sits nursing a single cup of tea and possibly a doughnut. At the start of each episode it seems, he is saved only by the arrival of the journalist, Polly.
What none of the customers know is that the “man in the corner – we never learn his name – is one of England’s finest detectives. Polly brings him details of cases that are baffling the police and he questions and probes her, encouraging her to sift through what she knows. Between them, they solve the cases without moving from the corner of the tea room.