Would you agree that Franklin Blake is the central character of the book? From what Wilkie has written in his Preface, as
PatH just quoted, his character determines circumstances too, as much as Rachel's does, don't you think?
What might Rachel have done? For starters, she could have stopped Franklin in the act, as soon as she saw him take the stone. His trance state would have been obvious and Mr. Candy would have confessed to dosing him in the morning. But, we wouldn't have a plot then, would we?
JoanK - I think you're right...Mr. Betteredge and Mr. Bruff are of another generation - capable of change though, as we see both of them charmed by Ezra Jennings. Poor Jennings, a terminal illness, an addiction, and now the loss of his only friend in the world. More sympathetic a creature than Rosanna, in my opinion - both smitten by the charming Mr. Blake.
Jonathan, I meant to thank you for fixing the image in my mind, of Rosanna's scheme to lure her beloved - so close, right over the Shivering Sands where her body lay. Collins' readers must have been swooning over this!