Octavia Plumb commands the Blighters in Southwark in Assassin's Creed Syndicate and is the leader you take down in Gang War: Southwark. She keeps a crowd of allies around her and lets them do most of the fighting.
The twins eliminate Plumb in the Southwark gang war, giving the Rooks the borough.
Southwark, the borough at the centre of the city's industry, has to be loosened before Plumb will fight. You remove the Templars Phillip Beckinridge and Myrtle Platt, take the strongholds at the Mint and Jacob's Island, kidnap the bounties Anna Abramson and Albie Vassell, and free the children in the Blackburn Bellows, Hightower Coal and Southwark Spinning Mill factories.
According to the messenger, Plumb accepts the gang war only grudgingly, with all weapons permitted. If you killed her beforehand he says her Blighters go into the fight without a leader and the Rooks are favourites. When she does join, her line is that the twins slaughtered her friends and she means to do the same to them, which fits a leader who has always relied on the people around her.
Bloody Nora
Bloody Nora is the Blighter leader of the City of London in Assassin's Creed Syndicate and the boss you face in Gang War: City of London. Her nickname comes from the ruthless violence that won her a place in the gang.
Cletus Strain
Cletus Strain runs the Blighters in Lambeth for Crawford Starrick and is the leader you fight in Gang War: Lambeth in Assassin's Creed Syndicate. He has a taste for theatrics and likes to smother enemies in smoke.
Crawford Starrick
Crawford Starrick is the main antagonist of Assassin's Creed Syndicate: Grand Master of the British Templars and the industrialist who controls London in 1868 through his factories, railways, banks, the Blighters gang and a ring of Templar lieutenants. Every major target the Frye twins kill is one of his people, and the main story builds toward a final confrontation with him at Buckingham Palace.
David Brewster
Sir David Brewster is the Scottish scientist and Templar experimenting on an Apple of Eden in a hidden laboratory under a Croydon train yard. He is Evie Frye's first target in Assassin's Creed Syndicate, in the memory A Simple Plan, whose optional objectives include air assassinating him.