When Twilight is called back to Canterlot to see to certain serious Princess duties, her friends seriously miss her. However, Rainbow has conflicted feelings, due to something that she thinks happened the night before her departure. So, when Twilight summons her - and her alone - to Canterlot, with instructions not to tell her other friends, she doesn't know what to expect. Certainly not being sent on a mission of national security with the fate of two worlds at stake, which becomes the start of an adventure of a lifetime.

One thing's for sure. That's the last time she agrees to one of Applejack's drinking games.