In Assassin's Creed Syndicate, Jacob Frye seeks to free London from Templar control.
The game is set in Victorian London in 1868, during the Industrial Revolution. Jacob and his twin sister Evie Frye arrive in the city and build an Assassin network to challenge the Templars and their allies. Their campaign moves through districts shaped by factories, railways, docks, crowded streets, and sharp differences between social classes.
Jacob generally focuses on direct action and gang warfare, while Evie is more closely associated with stealth, artifacts, and the search for the Piece of Eden known as the Shroud of Eden. Players can switch between the twins during much of the story, although some missions are assigned to a specific character.
Paris is the setting of Assassin's Creed Unity, and Boston is a major setting in Assassin's Creed III. Those cities belong to different historical periods and protagonists, not Syndicate's London campaign.