The Stolen Prince of Cloudburst by Jaclyn Moriarty
Long ago, the little Prince of Cloudburst was stolen from the seashore by a Water Sprite. Now, ten years later, the prince has found his way home. The King and Queen are planning the biggest party in their Kingdom's history to welcome him.
Meanwhile, on the other side of the Kingdoms and Empires, Esther Mettlestone-Staranise is looking forward to another year at Katherine Valley Boarding School. But she arrives to find a number of strange and unsettling changes. For one, her new teacher is rumoured to be an Ogre. Two mysterious students have joined the school, and one of Esther's classmates is an undercover Spellbinder. Most disturbingly, the mountains surrounding the school - usually a delight of glaciers, teashops, lakes and Faeries - are now crowded with wicked Shadow Mages.
As secrets and dangers escalate, Esther must find the answers to several puzzles. Why is her teacher behaving so oddly? Which of Esther's classmates is the Spellbinder, and can they really protect the school from gathering hordes of Shadow Mages? Could the Stolen Prince of Cloudburst be connected?
How can Esther - who is not talented like her sisters, nor an adventurer like her cousin, but just Esther - save her family, her school and possibly her entire world?-Goodreads