The Sunken Kingdom #1: Ghost Ship

EVER SINCE EMPEROR Flood drowned their kingdom and overthrew their parents, Asa and Rollo have been hiding out in Two Hills Keep. Then a mysterious stranger tells them their baby sister wasn’t killed along with their mother and father. Instead, she was kidnapped by Flood’s half-sister and secreted away in a castle to the north. If Una is still alive, there’s only one thing for Asa and Rollo to do. They must take Northseeker , an invisible ship built of mist and shadows, and cross the danger-fill