A mysterious virus has invaded Equestria. The only thing known about this virus is that it is a parasite that will latch onto a pony and put them into a euphoric state called The Bliss. Once in this state, the Pony will have no will to eat or drink and will die of thirst or hunger. The virus then absorbs the pony's nutrients.
Fast forward into the future.
Ponyville has been shut off from Equestria, and is guarded by a sturdy metal wall that stretches around the town. All are told not to leave the wall, by risk of death. However, as the population grows, a group of friends have to venture outside to find a larger place to move the citizens to.