Double Cross by Malorie Blackman

In a society divided by race and power, an ambitious Nought teenager determined to escape poverty and build a future with the girl he loves is drawn into the orbit of rival gangs. What begins as a quick way to earn money spirals into a perilous double game of loyalty and betrayal, forcing him to navigate escalating violence and moral compromise. As the stakes rise, he must decide how far he will go to protect those he cares about and whether he can break free of a system built on prejudice and fear.