For some reason, Twilight never got around to emptying her old Canterlot residence, and the Archives are fed up. She has until sunset to pack and leave. And for the first time in her life, she doesn't seem to be paying attention to the deadline.
The second anniversary of the Return is approaching, and all Luna wants for the celebration is one thing -- something Equestria hasn't seen in more than a thousand years. This could be a problem.