Halcyon: A Sentinel Novel

Parallel universes, an invasion of Earth, and eternally youthful sentinels. Nothing is as it seems at University School. Hailey Schick is used to being the new girl, but when she angers the dominant clique, her dreams of a normal school year are dashed. To make matters worse, Trevor, the boy she's falling for is a social pariah. When eternally young sentinels from a parallel universe infiltrate the school, it's up to Hailey and Trevor to stop them. But how are a pair of teens who can barely handle high school drama supposed to save Earth?