Canterlot, the present day.
In Canterlot Castle, inside the Library of Magic, there is one special wing where the most powerful and dangerous of spells are stored. This wing is kept locked at all times, and only the Princesses, and the Princess's personal student, are allowed to enter it freely.
“The Star Swirl the Bearded wing,” Celestia said to Twilight Sparkle as she scanned along a bookshelf. “The archmage had a rare combination of attributes: the power to wield the strongest of magics; the knowledge to explore the innermost workings of magical craft; and the foolish courage to perform experiments most ponies would never dare. For good reason.”
Twilight gulped, wondering if some suggestion of disapproval of her own magical work lay buried in her teacher's words. “You mean Star Swirl's work was... unethical?”
“That... is a debate that raged for centuries, Twilight. To tell the truth, I do not know. Illegal, however? Most certainly. But that is a question of diplomacy and legalisms rather than of ethics. Ah, here it is.”
Celestia had opened a large wooden chest in a far corner of the wing, and retrieved a smaller chest from within it. The small chest was made of silvery metal, and its surface was ornately engraved and inscribed with arcane script surrounding the slim keyhole.
The Princess placed it on a nearby writing desk. “Tell me, Twilight, what do you know about Star Swirl's mission in Saddle Arabia?”
“Actually, nothing, Princess,” Twilight admitted. “That is to say, I know that he had one. Clover the Clever mentioned it in her biography of him, but she didn't give any details to speak of. She only said that Star Swirl took what he found there and used it to create the Amniomorphic Spell.”
Princess Celestia nodded. “There is a reason nopony remembers exactly what happened there. It's not a terribly uplifting reason.” Her voice was lower now, tinged with a note of regret. “In hindsight it became clear that Star Swirl's voyage to Saddle Arabia was his first true great triumph, a sign that he was a legend in the making. But at the time, his trip was notable only because it was a diplomatic disaster, a tremendous embarrassment to me and my diplomatic corps.”
Celestia shook her head softly. “I wish I could tell you that when he returned I realized I had been wrong about him, but that would be a lie. Instead I was all too eager that nopony discuss the matter at all and let it lie forgotten, and in Saddle Arabia... well, let's just say that they had far more immediate matters to think about. There was, in the end, just one single written chronicle of what had happened.”
Here Celestia opened the silvery chest and retrieved a small, weathered book from inside it. It was a paperback, cheaply bound, and the image on its front cover was faded almost to the point of inscrutability, but Twilight detected powerful preserving enchantments that had kept it from aging for several centuries at least.
Twilight Sparkle's jaw dropped as she read the title. “The Caves of Maretania: A Star Swirl the Bearded Adventure Book.”
Celestia nodded, with a smile. “A very loose retelling. Clover the Clever was kind enough to give it to me late in her life. This was her own personal copy, and I believe it is the only copy that has survived. At the time, there was a whole series of them, though to be honest, they were rather badly written. But this was the first.”