An imposing, isolated hotel, high up in the Swiss Alps, is the last place Elin Warner wants to be. But she's taken time off from her job as a detective, so when she receives an invitation out of the blue to celebrate her estranged brother's recent engagement, she has no choice but to accept.
Arriving in the midst of a threatening storm, Elin immediately feels on edge. Though it's beautiful, something about the hotel, recently converted from an abandoned sanatorium, makes her nervous - as does her brother, Isaac.
And when they wake the following morning to discover his fiancée Laure has vanished without a trace, Elin's unease grows. With the storm cutting off access to and from the hotel, the longer Laure stays missing, the more the remaining guests start to panic.
But no-one has realized yet that another woman has gone missing. And she's the only one who could have warned them just how much danger they're all in . . .