Lydia Bentley has heard stories about the Montauk Project all her life: stories about the strange things that took place at the abandoned military base near her home and the people who've disappeared over the years. Stories about people like her own great-grandfather.

When Lydia stumbles into a portal that transports her to a dangerous and strange new reality, she discovers that all the stories she's ever heard about the Montauk Project are true, and that she's in the middle of one of the most dangerous experiments in history.

Alongside a darkly mysterious boy she is wary to trust, Lydia begins to unravel the secrets surrounding the Project. But the truths behind these secrets force her to question all her choices-and if Lydia chooses wrong, she might not save her family but destroy them . . . and herself.