Sherlock Holmes and Doctor John Watson are returning to London from Bucharest after the great detective has interceded in a delicate matter relating to the Rumanian Royal House. As they depart from Bucharest they receive their mail forwarded from London. Doctor Watson opens a distressing letter from his niece, Mina, now living in Budapest with her young husband, Janos, a newly qualified lawyer. It seems that the young man has not returned from a business assignment in Transylvania.
Holmes advises that he and Watson should postpone their return to Baker Street. Watson wires ahead and they are met at the station by Mina and her friend, Lucy Westenra.
Holmes is duly intrigued by their stay overnight at the home of Dr Westenra in the grounds of the asylum of which Dr Westenra is the Administrator.
Holmes suspects that letters from the young lawyer may have been forged, or written under duress. Next day they set off for Castle Dracula.