The show’s casting diversity is its most immediately striking quality, not just in Black aristocratic characters like the duke and Lady Danbury, but also in the entrepreneurial Madame Genevieve Delacroix (Kathryn Drysdale) and the working-class couple Will and Alice Mondrich (Martins Imhangbe and Emma Naomi). All of them are central to the complicated social caste system in the show’s version of early 1800s London.