It is spoken in legends of Equestria, that on the total lunar eclipse, a gateway to lands of myth and fiction would be opened. Twilight Sparkle, being a pony of science, does not believe this. But, she may be forced to believe the legend.

After learning of supposedly mythical creatures; and then seeing one, she learns of a foreign royalty using the gate to capture mythical creatures, and of how the voyage carrying those creatures was doomed from the very start. But this newfound knowlege is dangerous to her and everypony around her; and the swarms of horrors are gathering.