An enormous snow-covered mountain has appeared in the Pacific Ocean. No one knows when exactly it showed up, precisely how big it might be, or how to explain its existence. When Harold Tunmore is contacted by a shadowy organization to help investigate, he has no idea what he is getting into as he and his team set out for the mountain.

The higher Harold's team ascends, the less things make sense. Time moves differently, turning minutes into hours, and hours into days. Amid the whipping cold of higher elevation, the climbers' limbs numb and memories of their lives before the mountain begin to fade. Paranoia quickly turns to violence among the crew, and slithering, ancient creatures pursue them in the snow. Still, as the dangers increase, the mystery of the mountain compels them to its peak, where they are certain they will find their answers. Have they stumbled upon the greatest scientific discovery known to man or the seeds of their own demise?

Framed by the discovery of Harold Tunmore's unsent letters to his family and the chilling and provocative story they tell, Ascension considers the limitations of science and faith and examines both the beautiful and the unsettling sides of human nature.