There are only three survivors of a shipwreck off the Scottish Island of Stroma following one of the clearances of a highland glen in 1819. They are two very new babies and an eleven-year-old boy, Rory-Beag, sharp of memory but unable to speak due to a deformity from birth. He is cared for by a minister on the mainland of Caithness and the babies, assumed to be twins, are sent away and adopted by a couple from distant Northumberland, where they are baptised Kenneth and Kate and passed off as the adoptive parents' own children. Rory-Beag is the only person alive who knows that they are not even brother and sister, but he can tell no one until the minister teaches him to read and write. Desperate to find the twins, he makes two unsuccessful journeys to trace them, one when he is only thirteen and one as an adult. He fears they may be forever lost to him. In Northumberland, Kenneth and Kate grow up under their obsessive father, Ridley Reid, and ineffectual mother, Clara. The children long to kick over the traces but only Kenneth breaks away, first to school and then to the merchant navy. Separately, as young adults, Kenneth and Kate have cause to doubt the story Ridley and Clara have told them about their birth, but unless they break free of the hold of their parents, they may never learn the truth of their birth or the existence of the one who can solve the mystery found only in the memory of Rory-Beag.