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Several decades after the heroic actions of Jigsaw, Tiptoe, and Incendia restored the princesses, the world has begun the slow process of healing. Spectrum is a headstrong young stallion from Totemhoof who signs up with an excavation team in the hopes of experiencing a life changing adventure. What he finds will send him into a head-on collision with forces he can't begin to comprehend- and, perhaps, a chance to fulfill his destiny.

Sequel to Antipodes- though you don't need to have read it to enjoy this, I hope.

Set in the far future after Celestia and Luna mysteriously vanished and the sun and moon froze in the sky, Antipodes is the story of two ponies thrust out into the harsh new world on an adventure to uncover what happened to the world so long ago.