On Netflix, the episode is titled "Pact of the Dragon".
After getting into a fight in class, Akko and Amanda have detention together: They must clean the New Moon Tower, where they find dragons.
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An argument between Akko and Amanda in the midst of potions class triggers the explosion of one of the class' concoctions, causing them both to get detention. While cleaning the academy's tower as part of their punishment, the two girls witness a horde of dragons carrying off the Sorcerer's Stone. Strangely, the academy staff does not react to this theft, instead accidentally revealing that this is part of an anticipated prophecy involving a dragon. Lotte recalls the legend of a white dragon who resides in the nearby Ruins of Rastavan, which inspires Akko and Amanda to retrieve it themselves. Accompanied by their friends, they proceed to the ruins, where they discover that the culprit is a loan shark dragon named Fafnir, who has repossessed the Sorcerer's Stone from Luna Nova for their failure to pay off their debt. Luckily, Diana is able to decipher that Fafnir's promissory note (written in dragon language) does not actually mention paying back interest, meaning Fafnir had tricked the school into paying back more than they actually owed. Caught in his deception, Fafnir is forced into nullifying the contract and returning the Sorcerer's Stone to Luna Nova.