At the top of the world's tallest mountains, there isn't enough oxygen to breathe. In the space of hours your body begins to shut down. Any longer, and death is inevitable. What better place for a serial killer to find their next victim? Struggling journalist Cecily Wong is delighted to be invited to interview famed mountaineer Charles McVeigh, conditional on joining his team on one of the Himalayas' toughest peaks. But on the mountain, it's clear something is wrong. It begins small - a theft, an accidental fall. And then a note, pinned to her tent in the night: there's a murderer on the mountain...