Long Bright River by Liz Moore

Kacey lives on the streets in the vise of addiction. Her sister, Mickey, walks those very same Philadelphia blocks on her police beat. They don't speak anymore, but when Kacey disappears at the same time that a mysterious string of murders begins, Mickey becomes dangerously obsessed with finding her and the culprit, before it's too late.

Alternating its present-day mystery with the story of the sisters' childhood and adolescence, Long Bright River is at once heart-pounding and heart-wrenching; a gripping suspense novel that is also a moving store of siblings, addiction and the formidable ties that persist among place, family and fate.