This story is a sequel to The Knight and the Knave
With Princess Luna free of the Tantabus, Princess Celestia is ready to reveal an ancient secret to her sister and Twilight Sparkle: she is missing a large swath of her memories. Celestia has been unable to restore them by herself, so she will need the help of her friends to recover the missing details of her past.
Unfortunately, some buried things were not meant to be unearthed.