"You know something about radiation, don't you?"
It was perhaps the last thing that Celestia, protégé of Queen Harmony, was expecting her mentor to ask. Having a cutie mark related to the sun didn't prepare her for an expedition to the ocean floor to investigate a strange signal and then decide if the source should be salvaged. In the depths, Celestia makes a discovery that could change ponykind forever and she struggles with the implications as the full weight of responsibility begins to press down. Equestria's future will depend on her decision.