Looking back on it, the amount of confusion and misunderstanding at the beginning is almost absurd. Did Colonel Herncastle leave his niece, Rachel, the diamond out of spite or in good faith? No one knows. Rachel thinks that Franklin Blake stole the Moonstone, because she saw him do it. Franklin thinks Rachel is just being unfair, because he doesn't remember taking it. Neither of them knows that the doctor and Godfrey Ablewhite sneaked some opium into his bedtime brandy. Sergeant Cuff suspects that Rachel had a hand in stealing her own diamond, and that Rosanna Spearman was in on it. Rosanna thinks that Franklin Blake can't stand the sight of her, when he's really just clueless. Everyone thinks that Godfrey Ablewhite is just the greatest thing since sliced bread. We could go on, but you get the picture.
You might have thought that the confusion was bad enough from the outset, but then it gets worse! Franklin Blake thinks he's about to discover who took the diamond when he finds the hidden nightgown…but it's his own nightgown! Does this mean that he stole the diamond? He doesn't remember stealing it, so he asks Rachel. Sure enough, she saw him take the diamond with her own eyes. How on earth could this have happened?
No one could have guessed this outcome. Franklin Blake did, indeed, take the diamond, but he was drugged with opium at the time, and that's why he doesn't remember doing it. And then it was Godfrey Ablewhite, who appeared to be such a great guy, who actually took the diamond and pawned it in London in order to pay off his debts. Now that everything has been made clear, Franklin and Rachel are free to get married and live happily ever after.