魔法使い・キーフリーの弟子となったココは、同じアトリエで魔法を学ぶアガットとリチェの「第2の試験」に付き添いで同行します。そこに、禁止魔法を使う「つばあり帽」の妨害が入り、窮地は脱しますが試験は中断、キーフリーは負傷してしまいます。魔警団のメンバー・ルルシィと共に魔法使いの住む海底の「大講堂」に向かった一同は、三賢者の一人ベルダルートと面会し、再試験を受けることに…！

Coco and her peers follow Olruggio and Luluci as they deftly ferry a wounded Qifrey to the underwater Great Hall where witches gather. To their surprise, Beldaruit of the Three Wise Ones awaits the young apprentices at the bottom of the ocean... And he's willing to offer another trial after Agott's and Richeh's was cut short. But the spells and tests of Beldaruit are as much a mystery to unfold as his past, and Coco may be the only one who can put the pieces together and close in on the startling truth...