Although she is sad that she has to give up the pony she has outgrown, Steph is soon distracted from her own problem when she meets Comet, a magical pony who needs her help to find his twin sister.

It's been three months since the Winterians were freed and Spring's king, Angra, disappeared--thanks largely to the help of Cordell. Meira just wants her people to be safe. When Cordellan debt forces the Winterians to dig their mines for payment, they unearth something powerful and possibly dangerous: Primoria's lost chasm of magic. Theron sees this find as an opportunity -- with this much magic, the world can finally stand against threats like Angra....