Arc 27The Black Lake Task
William and Hermione spent the Yule Ball and Christmas together before preparing for the Second Task. Hermione finished first, but William's intervention in the Black Lake brought him into conflict with Vivian and left him troubled by her warning about Death.
- William and Hermione danced at the Yule Ball, kissed on the Hogwarts roof, and spent Christmas at their cottage, where Hermione solved the Golden Egg's underwater clue.
- William unlocked the Book of Alchemy's third volume with the Holy Grail, and he and Hermione used its instructions to build a Portkey door.
- William helped Cedric decipher his egg, while Hermione enlisted Trene to map the Black Lake and prepared for the underwater task.
- Ron overslept and was disqualified, while Hermione reached the Merpeople village by concealed boat and rescued William in twenty-five minutes.
- Cedric tricked Krum into meeting the mermaid princess in his place, and William and Hermione returned to help Cedric and Cho escape her pursuit.
- William defeated the mermaid princess and took her trident, which drew the Goblin Gems to him and summoned the Lady of the Lake.
- William restrained Vivian with the Holy Grail and Merlin's incantation, refused her offers for the gems, and heard her claim that the holders of the Deathly Hallows were marked by Death.
- Hermione placed first again, Dumbledore stopped a brawl after the scoring, and Rita exposed Ron's false account before William and Hermione withdrew from public view.