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.