The Thirteenth Key

In the winter of 1998, Gu Chuan, a university mathematics lecturer, receives an invitation to the reading of a will at Wuling Manor.

The manor's owner, Ye Shenwu, has died, leaving behind twelve keys and one strange condition: all twelve heirs must be present and turn their keys at the same time to open the underground archive.

After a blizzard cuts off the mountain, the first body is found inside the archive.

The door is sealed from the outside, there are no windows, and everyone still has their keys. They all think it's a perfect locked-room mystery, until Gu Chuan realizes they've misunderstood the door from the very beginning.