Never Gamble Your Heart by Lindsay Lovise

When the genteelly born, impoverished Frankie Turner’s impulsive younger sister goes missing, Frankie has no idea where to begin the search to find her. But when she discovers hasty marriages materializing between “troublemaking” women and men who don’t deserve them, she knows her sister is somehow involved. The only thread connecting the groomsmen is a membership to Rockford’s, an exclusive gambling hell owned by the devilish Jasper Jones. And it just so happens that Jasper has recently become the guardian of a sullen fifteen-year-old.

Jasper suspects his new governess has an ulterior motive for being in his household, but he can hardly find the time to uncover it when his life is in a constant uproar. First, Frankie teaches his niece how to count cards and then she tries to break into his study. When he finally learns Frankie’s true reason for being there, he agrees to help the brilliant mathematician find her missing sister, even if it means giving her a fake dowry and watching men trip over themselves in her presence. As he and Frankie work together to dismantle a nefarious scheme, Jasper realizes that for the first time in his life, he’s gambled his heart—and possibly lost it.