After Hook's death, the heroes decided to head to the Underworld to save him, dragging Rumplestiltskin along with them. When they arrived, however, they realized that saving Hook, and even getting themselves home wasn't going to be a simple matter of true love's kiss. Still, they persevered and after helping many denizens of the Underworld move on, along with condemning some to torment forever, they managed to defeat the mighty Hades and return to the world of the living. However, they didn't come back alone- many of the formerly dead followed them to Storybrooke, a weakness in the magic after Hades' defeat granting them a second chance at life. Among these beings was a dark and sinister evil that had been biding his time in the depths of hell until the right moment to make his return. A moment that came when the foolish heroes of Storybrooke ventured into a realm they didn't fully understand and played with the rules of life and death. This ancient evil was known as the Horned King, though his mighty name faded into obscurity from so long in oblivion.
Now free, the Horned King quickly sought to reunite with his source of power- an evil cauldron that had been stored in a forgotten realm for safe keeping. This realm, known as the Land of Untold Stories, quickly fell under the dominion of his might. Using the power of his almighty cauldron, an enchanted item that had been collecting darkness for thousands of years, the Horned King went back to his original mission- to rid existence of all realms beyond one of his own making. That meant accessing and destroying each and every unwanted kingdom.
Meanwhile, in Storybrooke, things returned mostly to normal. The formerly dead went about trying to find their places, both good and evil. Many looked to mend their ways, while others were eager to get back to the same tricks that got them killed the first time. Many others simply wanted to figure out about the strange new realm they found themselves in, and have a normal life. On the whole, though, it was a bit of a reprieve from chaos as everyone settled in. Naturally, it wasn't to last.
Portals have started appearing at random, staying open from minutes to days, leading to realms both old and new, and seemingly coming from no where. Even the darkest of Dark Ones claims to have no idea where the portals are coming from, or if they're going to stop. These portals have been stealing people away from Storybrooke as well as dumping unsuspecting people from distant lands into the town they know nothing about.
The portals were only the start of the problems. After that, those with magic started to feel a dark foreboding in the air- some even had visions of great decay and suffering. Death was ripe in the air.
Deep beneath the city, further down than even the mines, a cavern lurked. Expansive and dark, it served only to house water accumulated over time. Not even creatures made it down so far. It was in this cave that a portal had opened. Unlike the others, it's much like a black hole, deep and menacing, crackling endlessly with powerful magic that never ends. Never closes. From this portal, a large, cloaked figure had appeared, his skeletal features marred by darkness. Only two glowing red eyes cast light in the underground. He had arrived.
The Horned King had come to Storybrooke.
First, he created a castle beneath the town, in that deep cavern, out of reach of the citizens of Storybrooke. Then, his magic attacked the town, the undead coming knocking. These skeletal, mindless minions care only to kill, and cannot be reasoned with. They can, however, be killed with a good smash to the skull. But with attacks becoming more and more frequent, how long will it be until the town is fully over-run by zombies? Where do they come from, and how can they be stopped for good?
Some of the citizens, frightened by the zombies attacking the place, attempted to flee the town by crossing over the barrier and starting a new life in the Land Without Magic. However, once they stepped over the line, their lives ended, the helpless victims decaying down to skeletons and scraps of clothing. The Daily Mirror was quick to report the deaths, alerting the public to the danger of crossing the town line.