Sapphire and her brother Conor in Helen Dunmore’s novel ‘The Tide Knot’ are unable to forget their explorations of Ingo, the enigmatic underwater realm. They yearn to see their buddies from Mer again. But deep beneath the ocean’s surface, where the wisest Mer, Saldowr, watches over the Tide Knot, a crisis is building. Sapphire and Conor will soon be pulled into Ingo’s turbulent seas.