Ch. 421The Dementors' Overtime Pay (Third Update!)
William and Hermione tracked Black while investigating a hidden mole who had lured the Dementors toward Hogwarts. They drew most of the Dementors into a concealed room and sent a Patronus to warn Dumbledore, but one Dementor wandered off toward a cabinet beside a diadem.
- William and Hermione watched Black enter the Gryffindor Common Room, but chose to focus on stopping the Dementors from invading the castle.
- William suspected Tom's mole had lured the Dementors inside and found that the person had hidden their name and concealed themselves with a Disillusionment Charm.
- William and Hermione flew to the school gate and watched more than three hundred Dementors converge on the castle.
- William and Hermione released their captured Dementor's cries as bait and lured the others into a concealed room on the Seventh Floor.
- William sent a silver sea eagle Patronus to warn Dumbledore, then sealed the room with Hermione.
- One Dementor slipped away from the group and found a soul's scent near a broken bust and a dull diadem.