Cash in Hand by TA Moore

The last monster died a hundred years ago. At least, that's what the monsters want you to think.

Half-monster Cash just wants to keep his head down and raise his daughter, Ellie, to be an upstanding member of monstrous society. Even if she'd rather spend the summer with her human friends than learn the art of man traps at Camp Dark Hollow.

So the last person Cash wants to see is her uncle Arkady Abascal, who's also Cash's ex-boyfriend.

Arkady has more than Ellie's summer plans on his mind. He's there to enlist Cash to find out who's been selling monster secrets. Cash hasn't gotten any better at telling Arkady no, but it's not just his weakness for Arkady that makes him agree. The Prodigium thinks an Abascal exposed them to humans, and now the whole family is at risk-including Ellie.

Recruited to help Arkady identify the culprit-or frame a scapegoat-Cash finds the machinations of monstrous power easier to navigate than his feelings for Arkady. At least, at first. But when things get bloody, he wishes romantic disasters were all he had to worry about....