Cavanaugh's Surrender (Harlequin Romantic Suspense Series #1725)

Crime scene investigator Destiny Richardson receives the shock of her life when she finds her sister dead in a bathtub. Detective Logan Cavanaugh thinks it's an open-and-shut suicide case. But Destiny's convinced her sister was murdered. And she's not about to have some arrogant cop tell her otherwise—even if he is the sexiest man she's ever met.

Logan knows it's pointless trying to convince Destiny that it's against the rules to work on a relative's case. The crime scene investigator is as stubborn as she is gorgeous. Besides, Logan wouldn't mind getting to know her better. When it becomes apparent that there's a serial killer on the loose, Logan is bent on protecting the woman he's falling in love with.