In Arthur Conan Doyle’s “The Adventure of the Sussex Vampire,” the client’s first name is Robert.
Robert Ferguson writes to Sherlock Holmes because he believes his Peruvian wife, Mrs Ferguson, is attacking their infant son and drinking the child’s blood. The apparently supernatural allegation creates the story’s central mystery, but Holmes approaches it as a problem requiring evidence rather than a belief in vampires.
The story investigates the household relationships, the child’s condition, and the behavior of the family members. Holmes’s explanation replaces the sensational vampire theory with a human motive and a medical misunderstanding.
The story was first published in 1924 and later included in The Case-Book of Sherlock Holmes. The client is Robert Ferguson; his surname is sometimes remembered more readily because the story’s title names the Sussex setting rather than the family.