Skandar and the Chaos Trials

"To survive their third year of training, Skandar and his friends must complete a series of terrifying trials across the Island's elemental zones. Friendships, allegiances, and rider-unicorn bonds will be pushed to the limit--only the strongest will make it. Meanwhile, Skandar's sister Kenna has finally reached the Eyrie. But with a forged bond to a wild unicorn, she is alienated and alone. And when a terrible discovery puts the future of the Island in peril, all fingers point in one direction"--