The Baron and the Bluestocking by Nicole Bennett

Waltzes and Wagers
Five scandalous and supremely bored gentlemen. One silly gamble.
Trapped in what is perhaps the single dullest social season in all of England, the most infamous, and tight-knit, group of rogues in the Ton require a diversion. A frivolous wager to pass the time seems just the thing, and it doesn’t take the mischievous men long to concoct a little game. The task: waltz with a prickly wallflower of the group’s choosing by the end of the summer. Succeed and receive a great reward. Fail and complete a humiliating dare.