Harriet "Harry" Harrison, aka Madam Sapphire, is secretly running an out of hours brothel, "Blue" from a sleepy seaside town Police station (secret only to the bosses, newspapers and local Temperance league, but well known to its many customers including judges and other many pillars of the community). Business is booming and there is little crime in the town, as Blue keeps its customers too exhausted for other activities. But now the low crime rate has the station targeted for closure under Government cuts, and a visit from the new Police Commissioner threatens to axe any "dead wood." Harry, aided by a naive young Rookie, will go to hilarious lengths to avoid discovery of their secret activities and keep the branch open.