In the immediate post-war days of London, two unlikely partners have undertaken an even more unlikely, if necessary, business venture --- The Right Sort Marriage Bureau. The two partners are Miss Iris Sparks, a woman with a dangerous past in British intelligence, and Mrs. Gwendolyn Bainbridge, a genteel war widow with a young son entangled in a complicated aristocratic family. Looking to throw a New Year’s Eve soiree for their clients, Sparks and Bainbridge scout an empty building --- only to find a body contained in the walls. What they initially assume is a victim of the recent Blitz is uncovered instead to be a murder victim. To make matters worse, the owner of the building is Sparks’ beau, Archie Spelling, who has ties to a variety of enterprises on the right and wrong sides of the law, and the main investigator for the police is her ex-fiancée.

A happily married woman has come to the Right Sort Marriage Bureau to find a new wife for her husband. Dying of cancer, she wants the owners --- Miss Iris Sparks and Mrs. Gwendolyn Bainbridge --- to make sure that her entomologist, academic husband finds someone new once she passes. Shortly thereafter, she's found dead in Epping Forest, in what appears to be a suicide. But that doesn't make sense to either Sparks or Bainbridge. At the same time, Bainbridge is attempting to regain legal control of her life, opposed by the conservator who has been managing her assets --- perhaps not always in her best interest. When that conservator is found dead, Bainbridge herself is one of the prime suspects. Attempting to make sense of two deaths at once, Sparks and Bainbridge are once again on the case.

The Right Sort Marriage Bureau was founded in 1946 by two disparate individuals: Mrs. Gwendolyn Bainbridge, whose husband was killed in the recent World War, and Miss Iris Sparks, who worked as an intelligence agent during the recent conflict, though this is not discussed. Miss Sparks finds herself followed, then approached, by a young woman who has a very personal connection to a former paramour of Sparks. But something is amiss, and it seems that Iris' past may well cause something far more deadly than mere disruption in her personal life. Meanwhile, Gwendolyn is struggling to regain full legal control of her life, her finances and her son --- a legal path strewn with traps and pitfalls.

In London, 1946, the Right Sort Marriage Bureau is getting on its feet and expanding. Miss Iris Sparks and Mrs. Gwendolyn Bainbridge are making a go of it. That is until Lord Bainbridge --- the widowed Gwen's father-in-law and legal guardian --- returns from a business trip to Africa and threatens to undo everything important to her, even sending her six-year-old son away to a boarding school. But there's more going on than that. A new client shows up at the agency, one whom Sparks and Bainbridge begin to suspect really has a secret agenda, somehow involving the Bainbridge family. A murder and a subsequent kidnapping sends Sparks to seek help from a dangerous quarter --- and now their very survival is at stake.

In 1946 London, Miss Iris Sparks and Mrs. Gwendolyn Bainbridge are the proprietors of The Right Sort Marriage Bureau. One day, Lady Matheson, a cousin of Gwen’s who works for the Queen in "some capacity," arrives in need of some discreet investigation. It seems that 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. Wanting to keep this out of the palace gossip circles, but also needing to find out what skeletons might lurk in the prince's closet, the palace has quietly turned to Gwen and Iris. Without causing a stir, the two of them must uncover any secrets in the prince's past before his engagement to the future Queen of England is announced.

In a London slowly recovering from World War II, two very different women join forces to launch a business venture in the heart of Mayfair --- The Right Sort Marriage Bureau. Miss Iris Sparks and Mrs. Gwendolyn Bainbridge are determined to achieve some independence and do some good in a rapidly changing world. But the promising start to their marriage bureau is threatened when their newest client, Tillie La Salle, is found murdered and the man arrested for the crime is the prospective husband with whom they matched her. While the police are convinced they have their man, Miss Sparks and Mrs. Bainbridge are not. To clear his name --- and to rescue their fledgling operation’s reputation --- Sparks and Bainbridge decide to investigate on their own.