5th Wheel by Kate Calloway

Private Investigator Cassidy James is deep undercover in a college drama department, and the curtain is about to go up - on a dress rehearsal for murder!!

A sadistic serial killer is abducting young women and leaving their mutilated bodies along Oregon's coastal highway. Kings Harbor policewoman Martha Harper believes the clues lead to a local college, but her superiors don't see it that way. Desperate for help, she turns to her best friend, Cassidy James.

Posing as a teaching assistant in the Theatre Department, the undercover investigator soon finds herself surrounded by a cast of intriguing characters, including the alluring Professor Lauren Monroe - whose talents, Cassidy will soon discover, are not limited to the classroom. But the more she learns about Lauren and the people around her, the more Cassidy suspects she's not the only one playing a role.