1222 metres above sea level, train 601 from Oslo to Bergen careens off iced rails as the worst snowstorm in Norwegian history gathers force around it. Marooned in the high mountains with night falling and the temperature plummeting, its 269 passengers are forced to abandon their snowbound train and decamp to a centuries-old mountain hotel. They ought to be safe from the storm here, but as dawn breaks one of them will be found dead, murdered.