When the light fades and the moon rises over Innistrad, humanity becomes the universal prey. Packs of werewolves are drawn out by the moon, their humanity washed away by animal rage. Vampire families bare their fangs at the scent of human blood. Hordes of walking dead lurch across the manors and moors, driven by an innate hunger for the living. Alchemically created abominations twitch to life in alchemists' laboratories. Geists haunt the huddled human towns and terrify travelers along the dark crossways in between. From Innistrad's depths, powerful demons and impish devils plot humanity's downfall.
The humans of Innistrad have done their best to fight back. They form torch-wielding mobs to cleanse the abominations with fire. They train specialized holy warriors called cathars to strike back against the supernatural horrors. Most of all, they brandish the power of the Church of Avacyn. The Church is named for its leader, the powerful archangel Avacyn who was created by the Planeswalker Sorin Markov to safeguard humanity and allow them to coexist with their predators.
Innistrad's last few years have been tumultuous. First the demon Griselbrand trapped Avacyn in the Helvault with him, weakening the strength of the rites that invoked her and lowering humanity's defenses against the horrors of the night. When the situation was at its worst, with zombie armies marching on the high city of Thraben, the Helvault was sundered and Avacyn was released. But no sooner had Avacyn restored some measure of peace and balance to the plane than a new threat began to spin Innistrad toward its doom.
Madness swept over Innistrad as the fleeting hope of Avacyn's angelic protection turned to horror. Sorin Markov finally intervened, unmaking his beloved creation. But with Avacyn's unmaking, the last protections over the plane fell as well, opening it to new otherworldly intruders....