In the story "The Adventure of the Sussex Vampire," Holmes is summoned to examine a case involving the second wife of a man named Ferguson. This wife, who is from Peru, has beaten Ferguson's son, Jacky, from his first marriage. Before Holmes visits Ferguson's house in Sussex, Ferguson tells Holmes that Jacky, or Jack as he is also known, has a twisted spine from an accident in childhood. Holmes deduces that Jacky is intelligent, even before meeting the boy, as the boy's body has been limited in what it can do. Therefore, Jack has turned to the life of the mind and has become very intelligent. When he visits Ferguson's house, Holmes confirms that Jack, jealous of his younger half-brother, is shooting darts filled with poison at the small child and that his stepmother struck Jack as a result.