Franklin learns that Dr Candy, the Verinders' physician, gave him laudanum as a sleeping draught on the night of the theft but Candy's successor Dr Jennings tells him it was more likely to have induced sleep-walking and suggests he take another dose to repeat his actions of the night. Under influence of the drug he is seen to have unconsciously taken the stone and recalls giving it to somebody else for safe keeping. A trip to London with Sergeant Cuff to visit Septimus Luker will expose the real thief, to whom Franklin gave the moonstone, reuniting Franklin with Rachel, before the moonstone is restored to its original home.
—don @ minifie-1