Helen Stoner consults Sherlock Holmes about the death of her twin sister, Julia, who died before her wedding, crying that: "it was the Speckled Band!"
Holmes must investigate their mother's estate and the unpleasant Dr Roylott, Helen's stepfather, who allows gypsies to camp on his estate and has both a cheetah and a baboon running amok in the grounds.
But can Helen be believed? Is Dr Roylott as bad as he seems? And can the specked handkerchiefs worn about the necks of the gypsies really be a coincidence?