"the possibilities for a Bill Sykes or a Mademoiselle Hortense"

Two of Dickens' villains:

Bill Sykes (or Sikes) is a character from Oliver Twist, a violent and barbaric criminal who is responsible for one of the most horrifying murders in Dickens' work.

Mademoiselle Hortense appears in Bleak House as Lady Dedlock's maid. Dickens based her character on the real-life case of Maria Manning, who murdered her lover in August 1849.