J. S. Volpe 
The Thing in the Alley [EPUB ebook] 

When horribly mutilated bodies start turning up in Kingwood, the Anomaly Hunters determine that the culprit can only be a leucrota, a supposedly mythical monster that can mimic people’s voices. With Violet’s history-geek sister Lauren helping out, the team combs the city in search of the man-eating beast. Will they stop the leucrota before it kills again, or will they only become its latest victims?
Plus, an unexpected discovery in Mr. May’s office leads Calvin to a young woman named Tiffany Fish who has strange links to both the Anomaly Hunters and their current investigation.