Long Bright River by Liz Moore (2019, Book of the Month)

"Two sisters travel the same streets, though their lives couldn't be more different. 
Then one of them goes missing.

In a Philadelphia neighborhood rocked by the opioid crisis, two once-inseparable sisters find themselves at odds. One, Kacey, lives on the streets in the vise of addiction. The other, Mickey, walks those same blocks on her police beat. They don't speak anymore, but Mickey never stops worrying about her sibling. 

Then Kacey disappears, suddenly, at the same time that a mysterious string of murders begins in Mickey's district, and Mickey becomes dangerously obsessed with finding the culprit—and her sister—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 story of sisters, addiction, and the formidable ties that persist between place, family, and fate." From StoryGraph