Sins of the Angels by Lydia M. Hawke

Homicide detective Alexandra Jarvis is up against a serial killer unlike any she’s ever encountered. She has neither time nor patience for the arrogant new partner assigned to her in the middle of the case, but he seems hellbent on getting in her way—and under her skin—at every turn.

A millennium ago, Aramael sentenced his own brother to eternal exile. Now the fallen angel is back and wreaking murderous havoc in the mortal realm, and it’s up to Aramael to stop him—and to keep the stubborn human police officer out of his path.

With tensions flaring between them and Alex’s uncanny ability to see him for who he really is, both Aramael’s mission and his soul are in serious danger. Can he and Alex work together to capture the fallen one? Or will Aramael end up committing a sin more unspeakable than that of his brother?