The father who seeks Holmes’s help in “The Adventure of the Sussex Vampire” is Robert Ferguson.
The story was first published in 1924 and later collected in The Case-Book of Sherlock Holmes. Ferguson writes to Holmes because he believes his Peruvian wife, Dolores, is drinking blood from their infant son. The apparently supernatural report is treated as a problem requiring observation rather than immediate acceptance of a vampire explanation.
Holmes investigates the household and discovers that the evidence has been misunderstood. The case’s resolution depends on family relationships, hidden motives, and a child in danger rather than on anything supernatural. Doyle uses the title to create a Gothic expectation while ultimately grounding the explanation in human behavior.
The story is one of the later Holmes cases and is sometimes remembered for its unusual subject rather than its relatively short investigation. “Sussex” identifies the setting, while Ferguson is the surname of the worried father.