Secrets of a Summer Night
Annabelle Peyton is a penniless aristocrat who must marry a titled gentleman to save her family from ruin. While she hunts for a suitable match among the London elite, she is pursued by Simon Hunt, a wealthy commoner who offers passion instead of a wedding ring. Annabelle and her three fellow wallflowers must navigate the social season to find security before her heart betrays her.
Secrets of a Summer Night is the first book in Lisa Kleypas's Wallflowers series. It introduces the four "wallflowers" — Annabelle, Lillian, Daisy, and Evie — who form a pact to help each other find husbands, and their friendship carries through the rest of the series, so reading in publication order starting here is recommended.
Yes. It's a historical romance with several sensual, "spicy" scenes between Annabelle and Simon, consistent with the tone of Lisa Kleypas's Wallflowers series overall.