The Chosen — Taran Matharu

Throughout history, people have vanished with no explanation. A group of teenagers are about to discover why.
Cade is settling into a new boarding school, contemplating his future, when he finds himself transported to another realm. He soon discovers their new world is populated with lost remnants from the past: prehistoric creatures, ancient relics, and stranger still―people. Overwhelmed by his new surroundings, Cade has little time to adjust, for soon he and his fellow classmates are forced to become contenders in a brutal game, controlled by mysterious overlords.

But who are these beings and why did they choose these teens? Cade must prepare for battle . . . because hiding is not an option.