Franklin Blake is a major character in the novel. He narrates significant portions of the plot, and takes a leading role in investigating the theft. Franklin functions as the romantic lead, since he ends up marrying Rachel and he is also, in a sense, the thief: Franklin takes the diamond in an opium-induced trance, although it is Godfrey Ablewhite who is responsible for trying to sell the diamond and profit from the theft.

Franklin is handsome and charismatic. Much of the conflict of the plot stems from Rosanna’s falling in love with him at first sight, and Rachel’s caring for him so deeply that she covers up what she believes to be criminal activity on his part. Since Franklin has travelled so extensively, he has a cosmopolitan and sophisticated nature, but he is also somewhat fickle: Betteredge describes how Franklin has “so many different sides to his character, all more or less jarring with each other, that he seemed to pass his life in a state of perpetual contradiction with himself” (48). Franklin can also be stubborn and antagonistic; the conflict of the plot largely stems from Franklin antagonizing Mr. Candy in an argument about medicine, leading to Candy secretly administering opium to him.