After his recent unveiling of a devious assassin, Sir Hugh Corbett has returned to service as the Keeper of the Secret Seal. Summoned to meet the King, Corbett and Ranulf learn of the death of Corbett's friend, Ralph Grandison. Ralph, a leper, has been found dead in a rowing boat, a dagger in his chest. But this murder is not the first of its kind. Other patients of the hospital, all former knights of the Royal household, are being targeted. The discovery that Ralph was killed by a poison dagger that once belonged with the Crown Jewels leads Corbett down a complex path, where the risk of disease plays out against the backdrop of finding an assassin who will use any means necessary to kill.