Citadel of the fallen
(Book)

A group of teenage students, while exploring deep within the rainforest, barely survive an encounter with a wild and surprisingly magical boar. In doing so, they discover that events that threaten to destroy their entire civilization have already been set into motion. The Black Tide, the annual rampage of millions of giant ants through the rainforest, has been coerced by the Demon Queen to take a path that will send it tearing through the farmlands that support the Citadel, their home. While the adults frantically race to prepare for the coming disaster, one of the teenagers who survived the boar attack, Malcolm, begins to experience violent visions of the past. He learns that he's no longer alone in his own body. His revelations lead the group of teenagers to discover that many of the leaders within the Citadel are similarly possessed.