The Five Orange Pips (The Adventures of Sherlock Holmes, Episode 5)

John Openshaw tells Holmes that in 1883 his uncle died two months after receiving a letter inscribed 'K.K.K.' with five orange pips enclosed, and that in 1885 his father died soon after receiving a similar letter; now Openshaw himself has received such a letter. Holmes tells him to do as the letter asks and leave a diary page, which Holmes deduces is connected to the Ku Klux Klan, on the garden sundial. Openshaw is killed before he can do so, but Holmes discovers the killers have been travelling on a sailing ship, and sends the captain a letter with five orange pips. The ship is lost at sea.