This story is a sequel to Doctor Whooves Episode 11: Parents' Day

The Doctor, Twilight, Derpy, and the others return to 1002 and arrive right in the middle of Canterlot a mere five minutes after their original departure. They arrive to find a troubled pair of alicorn sisters and an eccentric stallion who knows the Doctor well. However, they also come across a Dalek who has named Princess Luna as its next target.