"After saving the King of Sunkland, reuniting the thirteen clans of the Equestrian Kingdom, and defeating the High Priestess of the Chaos Serpents, Mia has finally returned to Saint-Noel for some much-needed respite...until that's interrupted by two girls magically appearing before her. If Bel wasn't enough, Mia must now also care for the mysterious Patricia. Just where did she come from? Bel doesn't seem to know, and the only clue they have is her last name: Clausius.

As Mia tries to dig into the girl's past, she discovers a terrifying truth. Patricia's education has been raising her into a Chaos Serpent! To keep this under wraps, Mia resolves to tell her a minor fib—she isn't Princess Mia Luna Tearmoon, but a teacher sent by the Serpents. Mia uses this pretense to raise the girl right, and somehow, it works! But as smiles begin to return to Patricia's lips, the case of a stolen sacramental item throws her morals into question...

"