Sherlock Holmes investigates a series of deaths at a castle with each foretold by the delivery of orange pips to the victims.
Holmes is visited by Mr. Chalmers, an insurance agent with a strange tale. Seven single men, calling themselves "The Good Comrades", live together in the remote Scottish castle of Drearcliffe House, near the village of Inverneill.
Recently one of the "Good Comrades" received a strange message, an envelope containing nothing but seven orange pips. That night, he was murdered and his body horribly mutilated. A few days later, a second envelope was delivered, this time containing six pips, and the recipient also died mysteriously soon afterwards, his battered corpse being recovered from the base of the cliffs. Chalmers holds £100,000 of life insurance policies on the seven men, and suspects that one is systematically murdering the others in order to collect the money, and begs Holmes to investigate.
Holmes and Watson arrive at the scene only to find another murder has occurred. His body is burned to a crisp. Lestrade also arrives to investigate. Despite Holmes' best efforts, three more deaths occur, each time leaving the victim's body unrecognisable.
Lestrade jumps to the obvious conclusion, that the last surviving member, Bruce Alistair (Aubrey Mather), murdered all the others. However, after Watson goes missing, Holmes has deduced the truth and leads Lestrade (and Alistair) to a secret room where all the "Good Comrades" - alive and well - are hiding with Watson tied up. Holmes explains that Alistair was the victim of a plot to frame him for murder and collect the insurance money by the other six.