In London 1946, The Right Sort Marriage Bureau is just beginning to take off and the proprietors, Miss Iris Sparks and Mrs. Gwendolyn Bainbridge, are in need of a bigger office and a secretary to handle the growing demand. Unfortunately, they don't yet have the necessary means. So when a woman arrives -- a cousin of Gwen's -- with an interesting and quite remunerative proposition, the two of them are all ears. The cousin, one Lady Matheson, works for the Queen in "some capacity" and is in need of some discreet investigation. It seems that the Princess Elizabeth has developed feelings for a dashing Greek prince and a blackmail note has arrived, alluding to some potentially damaging information about said prince.