Changeling by Yasmine Galenorn

We're the D'Artigo Sisters: Half-human, half-Faerie, we're savvy--and sexy--operatives for the Otherworld Intelligence Agency. But our mixed-blood heritage short-circuits our talents at all the wrong times. My sister Camille is a wicked-good witch whose magic is as unpredictable as the weather. My sister Menolly is a vampire trying to get the hang of being undead. And me? I'm Delilah. When I'm under stress, I transform into a tabby cat--and a series of violent murders is really getting me bent out of shape...
"Someone's been slaughtering the Weres of the Rainier Puma Pride, and my sisters and I have been enlisted to investigate by Zachary Lyonnesse, golden boy of the werepumas. Right away we smelled demon trouble, and we tracked it directly into the snare of the Hunters Moon Clan, sworn enemies of Puma Pride. But there's more than Were rivalry at work. It's that old demon Shadow Wing who is setting a deadly snare for the pumas. We have to find out why, which means a visit one to of the Immortals. Unfortunately, for my sisters and me, our half-human blood is just enough to put us in mortal danger." "At the Wayfarer Inn, a portal to Otherworld and the local hangout for humans and beasties alike, our fellow operative Jocko's been murdered. Every clue points to Shadow Wing, the soul-munching, bad-ass leader of the Subterranean Realms. He's made it clear that he aims to raze humankind to the ground, turning both Earth and Otherworld into his private playground. Our assignment: keep Shadow Wing and his minions from creeping into Earth via the Wayfarer. The demons figure they're in like Flynn. After all, with only my 'bumbling' sisters and me standing in the way, how can they miss? But we've got a secret for them: faulty wiring or not, nobody kicks ass like the D'Artigo girls."

This book is part of the "Otherworld/Sisters of the Moon" series.
Here are some other books from this series: