Olivia is the princess of Venice. So when the waters start to rise, she knows only her magic can prevent disaster befalling the city. Desperate for help, and for a friend, Olivia discovers something incredible: a water horse, hidden in the canals of the city. Invisible to most, Lucian knows the deepest secrets of the sea – secrets that could hold the key to saving the city. But can their friendship overcome those plotting against Olivia, and against Venice itself?