Derring-Do is an aspiring archaeologist studying the long fabled and mythical Lost Kingdom of Thule, a highly advanced civilization that mysteriously disappeared thousands of years ago beneath the depths of the ocean. The key to finding this lost civilization is the lost journal of Clover the Clever, said to have intricate instructions on how to get to Thule. Unfortunately for Derring, she has no evidence for either even existing.

That is, until a mysterious benefactor offers to fund an expedition and take her on her first, and possibly last adventure.

Basically, Disney's Atlantis: The Lost Empire with ponies.