Once, the Doctor traveled time with Star Swirl the Bearded, taking in the wonders of the universe as friends. However, some events are fixed, and Star Swirl had to leave so he could play an essential part in Equestria's history.
When the Doctor learns that Star Swirl faces a crisis of conscience, he will risk everything to be there for his old friend.
Pre-reading and editing by Moosetasm and OnionPie! Cover image stitched-together from here and here and here. Not connected to my other Derpy stories.