The Guardian Devil

As a ten-year-old boy, Alex Hays witnesses the rape and murder of his mother on a brutal South London estate run by a ruthless drug gang. After being adopted he spends the next decade learning all he can and training himself to take those responsible for his mother's death.
When his adopted sister is savagely beaten by he boyfriend, a member of the drug gang, Alex starts a one man war to bring them down, eventually leading to his mother's killer.