25 Days

Adam Gray books a cabin high on a snowbound mountain, hoping a holiday away from everything will pull his family back together. The isolation is the point. Then a gift turns up in the Christmas stocking hanging on the barn door, left by someone who was close enough to put it there.

Another appears the next morning, and the next. What starts as unsettling becomes unmistakable: the family has been entered into someone else's game, one that runs on a countdown and has rules they were never told. Getting off the mountain alive means playing.

Per Jacobsen's holiday horror novel works the classic isolated-cabin setup with an advent-calendar structure, tightening the screws a day at a time.