Blame It on the Duke by Lenora Bell

Nicolas, Lord Hatherly, never intended to marry—nor add to the mad Hatherly line—but now he must honor his father’s debt to a social-climbing merchant or lose the family estate. A notoriously wild marquess, won by her father at a game of cards, is the very last thing Miss Alice Tombs wants. She’s spent the last three seasons repelling suitors in spectacular fashion so she’d be at liberty to explore the world. She’ll just have to drive this one away as well.

Until Nick proposes an utterly tempting arrangement: one summer together to prove the legitimacy of their union, then Alice is free to travel while Nick revels in the time he has left before the Hatherly Madness takes hold. It will be easy to walk away after a few months of make-believe wedded bliss—won’t it? Alice and Nick are about to find out…one sultry night at a time. This ought to be fun…