This is not the Hogwarts you know. Certainly, its layout is identical, but its ghosts and professors have disappeared. Monsters roam the lower dungeons, and silent house elves dart about performing necessary duties. Outside, it is always winter; the enchanted ceiling of the great hall is always black, even in the daytime. Hogsmeade is deserted, the train doesn't run, and few who venture into the wider world ever return.
Hogwarts, however, is alive...in a way. People of all ages and from all times are beginning to appear, and they are told by a mysterious old man with no name that they have been rescued, though rescued from what is unclear. Now they must learn how to exist in this new world, with people who may have been dead or not yet born in their own time.
But all is not well in Hogwarts Castle. Who is the benevolent dictator ruling this world? Is he really that kind after all? What happens when monsters begin to rise to the inhabited levels? And what happens to the people who try to run away?