In Too Deep by Ronica Black

When undercover work requires working under the covers, danger is an uninvited bedfellow…

Erin McKenzie, a newly promoted homicide detective, lands the assignment of her career when she is chosen to investigate Elizabeth Adams, the number one suspect in a slew of serial murders. Adams, elusive and devastatingly beautiful, is not only an accomplished seductress but also a lesbian. Erin, straight and married, needs a crash course in more than just undercover detecting. With Patricia Henderson, a fellow homicide cop and Adam’s former lover as a mentor, Erin embarks on the journey of her life…with love and danger hot on her heels.