Colgate, Clockwork, Bright Eyes, Matilda, and a universally-displaced Daring Do travel to discover the hotspot of dimensional rifts in the Equestrian universe.
Why is Celestia calling for a stallion in a blue box? Why is princess Luna being seen throughout time and space with a mysterious colt? What does this have to do with Nightmare moon returning? Short answer: The Doctor.
Ever since Twilight Sparkle stumbled upon a bunch of pony-eating shadows, her life is changed forever. Especially after she meets a stallion who claims to be "The Doctor".