Confounding Oaths by Alexis Hall

A nobleman must work with a dashing soldier to save his sister from a mystical bargain gone awry in this swoon-worthy romance from the bestselling author of Boyfriend Material.

It is the year 1815, and Mr. John Caesar is determined to help his sister, Mary, successfully navigate the marriage mart. A high-stakes endeavor at the best of times, this task is made slightly more difficult by his family’s nontraditional background, the pernicious whimsof the ton, and the ever-present complication of living in a world full of scheming fairies and capricious gods.
Despite all that, John knows that his parents wish to see his sister comfortably settled. He also knows that the sooner he sees Mary’s future secured, the sooner he can get his own wish—returning to an aristocratic life of leisure. And as for Mary? Sweet, sensitive Mary just wishes gentlemen would pay as much attention to her as they do to her younger sister.
When Mary’s all-too-literal wish puts her squarely in the sights of a malicious fairy godmother, John sets out to save her. This choice throws him into the path of Captain Orestes James—the handsome up-from-the-ranks hero of Wellington’s armies—and his ragtag band of misfits. Together, John and the captain will venture into a vicious world of fey bargains and sacrificial magic as they draw ever closer to rescuing Mary—and to each other.
While John is no stranger to casual dalliances with soldiers, until now he’s never expected one to last—or wanted one to. He and the captain come from different worlds, and even if Orestes feels the same, John knows there’s no point in wishing for something more between them.

After all, John has learned firsthand that getting what you wish for can be a dangerous thing. . . .