The Winter Box by Tim Waggoner

Winner of the 2017 Bram Stoker Award for Superior Achievement in Long Fiction
It's Todd and Heather's twenty-first anniversary. A blizzard rages outside their home, but it's far colder inside. Their marriage is falling apart, the love they once shared gone, in its place only bitter resentment. As the night wears on, strange things start to happen in their house-bad things. If they can work together, they might find a way to survive until morning...but only if they don't open the Winter Box.