Celestia summons Twilight to Canterlot so they can study the nature of alicorn magic together. Joining her is another princess from the Cantoribbean Isles. A disturbance in the castle forces Celestia to leave while the other two continue their studies. Later, Spike reveals that Luna has gone missing. Twilight wants to abandon her studies to help but a growing rivalry between her and the other alicorn princess clouds her judgement. Can Spike talk some sense into her or will they be too late to save Luna?