Equipped with a burner phone and a new job, Cassie Peters has left her hectic and secretive life in New York City for the refuge of her hometown of Mammoth Lakes, California. There, she begins working again with Yosemite Search and Rescue, where a case she worked a decade ago continues to haunt her.

She quickly falls into old patterns, joining a group of fellow seasonal workers and young adventurers who have made Yosemite their home during the summer. There, she meets Petal, a young woman living in a trailer with her much older wife, keeping a detailed diary of the goings on of the park, and Jada, a recent college graduate on a cross-country road trip with her boyfriend, documenting their journey on Instagram.

When these three women cross paths, Cassie's past catches up with her, and the shocking consequences ripple out far beyond what any could have imagined in this unputdownable thriller from an author who "never fails to impress" (Mary Kubica, New York Times bestselling author).