His Wayward Bride by Theresa Romain

Everyone has secrets…

Though their horse-racing family is as troubled as it is talented, all of the Chandler siblings have found love…except eldest brother Jonah. Married four years ago and abandoned after his wedding night, single-minded Jonah now spends his days training Thoroughbreds—while his lost bride is a family mystery no one dares discuss.
And that’s just the way Jonah and his wife, Irene, want it.
The biracial daughter of a seamstress and a con artist, Irene has built a secret career as a spy and pickpocket who helps troubled women. By day she works as a teacher at Mrs. Brodie’s Academy for Exceptional Young Ladies; in spare moments she takes on missions that carry her everywhere from London’s elite heart to its most dangerous corners.
Jonah agreed to this arrangement for four years, until Irene’s family fortunes were made. After surviving on passionate secret meetings and stolen days together, now it’s time to begin the marriage so long delayed. But as these two independent souls begin to build a life together, family obligations and old scandals threaten to tear them apart…