Recovering their balance after their adventures in Lincoln and the discovery of their secret sister, Aventurine Morrow and her twin Micheline are holed up together in Hay-on-Wye. There, they receive several coded messages indicating the possibility that Mick's husband, Shep, lost at sea, might actually have died by suicide. When her twin disappears, Avi must join forces with the always-suspicious policeman Dominic Burroughs to decipher those clues...