Amulet: Prince of the Elves (Amulet #5)

Emily, Navin, and the crew arrive in the lost city of Cielis, but they soon realize it is not the utopia they expected to find. While Trellis and Luger are taken prisoner, Emily is forced to fight for her life in a series of tests that will determine who among the new generation of young Stonekeepers will join the Guardian Council, the powerful group of Stonekeepers who govern Alledia. As the number of competitors gets smaller and smaller, a terrible secret is slowly uncovered - a secret that will change the lives of our heroes forever.