Requirement

Hermione glared at him in annoyance, ready with her retort, and then- "You can't apparate anywhere on Hogwarts grounds, you dolt," Malfoy snapped at Smith. / Professor Peverell, Professor Black, Professor Gaunt... all have participated in a dark plot haunting the Hogwarts Halls. Hermione's return, and Malfoy's presence, may be all that stands to prevent a catastrophe.