Two Shades of Blue - Sydney Gibson - Bog

For Detective Lieutenant Emma Tiernan, murder's been her business for too long. Just as she's looking forward to early retirement, she is assigned a disturbing new homicide - and an unwelcome new partner, stretching her boundaries to their limit.
Beautiful rookie detective Sasha Garnier is as infuriating as she is impressive, and the combination wreaks havoc on Emma's careful defenses. The reluctant pair soon realize they have a serial killer on their hands, one who plays games only Emma seems to understand. As the case heats up, more than their professional relationship is put to the test.
When the FBI inserts itself into their investigation, secrets are revealed that cut Emma to the bone. It's a race against time to figure out who she can trust, before the murderer claims his next victim, likely, Emma herself...