Once upon a time a coupling snapped, and a TARDIS fell screeching through the Vortex. Once upon a time a Timelord cursed and made a forced landing on an obscure watery planet somewhere in the Milky Way.
Once upon a time a Timelord left her ship unattended and unlocked, and went out to search for some platinum and a mirror to fix the coupling.
Once upon a time two Earth teenagers were looking for a place to be alone, together.
Once upon a time a child was born on Earth who held all of time and space within her mind. A child was born who found her way from Earth to Gallifrey, and, though it took her hundreds of years, she had the time to do it in.
Once upon a time there was a Timelord on Gallifrey who longed to see the universe but who was too scared to run. Still, he saw it reflected in the eyes of his Earth-born Timelord wife.
Once upon a time on Gallifrey a child was born, to see the universe, and to remember Earth.