Unleashed: The Devil Between Us by Jessica Thompson

Tyler “Screech” McCabe has one rule: survive. For him and his little sister, Squeeks, that means enduring the fists and criminal demands of their stepfather, Danny.

Screech is a survivor, a shadow in the back alleys, his anger a tightly coiled spring.
Things take a turn when a girl with a ghost in her smile lunges into his world, and doesn’t flinch when he shows his teeth.
Their connection is a lit match in a gasoline-soaked world, volatile and dangerously addictive.
She has secrets darker than Screech’s own bruises, and when a final, brutal confrontation goes too far, the real monsters are unleashed.