Beneath the ice of our forsaken homeland is a magnificent subterranean labyrinth, a place of breathtaking wonders --- and terrors beyond imagining. A team of specialists led by archaeologist Amethyst "Sparkler" Star has been hoof-picked to explore this ancient place and uncover the secrets it holds.

But they are not the first to venture into the darkness --- and those they follow did not return.

There are mysteries here the predate the founding of Equestria, revelations that could change everything we thought we knew about the Great Winter and the mass exodus that followed. Because down here in the dark and warmth, something survived the ancient storm... a forgotten fourth tribe we left behind.