On a school trip to snowbound Scotland, several students become infected and turn into hungry zombies, leaving a small band of survivors to take refuge in the school bus.

Ivy Calhoun's life has been turned upside down. Her new stepdad has uprooted Ivy and her mom, bringing them to live in an actual castle in the misty Scottish countryside. There are stone-faced servants and shadowy corridors, and the ancient walls seem full of secrets. Ivy is at once frightened and intrigued. Especially when she meets Logan, a gorgeous, elusive ghost who has haunted the castle grounds for decades. Ivy is immediately drawn to him ....

In 1866, after her boarding school is destroyed, Corrine and two of her classmates travel to Scotland to retrieve the stolen rathstone from the Unhallowed, but when tensions arise among the girls, Corrine is uncertain in whom to put her trust.