An essential part of the English ecosystem, street gangs dominated the nineteenth century underworld. In an attempt to unify the street gangs under one regime, the Templar Order created the Blighters, and attempted to remove any opposing forces to their cause.
The Clinkers of Whitechapel, the last remaining independent gang in London, fought in vain against the mighty oppressors. Eager to turn things around, they welcome twin Assassins Evie and Jacob Frye into their circle. Proposing a new idea to take back the streets of London from under the Blighters' feet, the Clinkers took on the identity of the Rooks and decided to fight under the guidance of the Frye twins.
Their main approach to undermining the Blighter influence is to sabotage their hold on different areas in the city (such as Blighter-owned factories and strongholds) and then challenge them to a final fight for the territory in a gang war.
Nowadays, London doesn't really have street gangs like those. It's got students in bright jackets carrying clipboards who stop you and demand your credit card details instead.