When a mysterious tower appears in the skies over England, thirteen strangers are pulled from their lives to stand before it as a countdown begins. Above the doorway is one word: ASCEND.

As a grieving teacher, a reclusive artist, and a narcissistic celebrity children's author lead the others in trying to understand why they've been chosen and what the tower is, it soon becomes clear the only way out of this for everyone... is up.

And so begins a race to the top, through sinking ships, haunted houses and other waking nightmares, as the group fights to hold onto its humanity, while the twisted horror of why they're here grows ever more apparent - and death stalks their every move.