After the Second World War ends, former spies Josephine Daunt and Susan Dervish, played by Anna Massey and Imelda Staunton respectively, set up a detective agency
During wartime, Josephine Daunt, a Special Operations Executive operative in France, and Dervish, her controller in London, were engaged in exciting and dangerous work. But in peacetime they found themselves at a loose end. Though very different people - Daunt, Cambridge educated, meticulous and inquisitive, and Dervish, practical, energetic and instinctive - they work well together and form a private detective agency, enlisting the help of Bill Mackie, a former private detective, whose son had been killed in the war while working for SOE.