¡°Because the castle's protected by more than walls, you know,¡± said Hermione. ¡°There are all sorts of enchantments on it, to stop people entering by stealth. You can't just Apparate in here. And I'd like to see the disguise that could fool those Dementors. They're guarding every single entrance to the grounds. They'd have seen him fly in too. And Filch knows all the secret passages, they'll have them covered¡¡±
Lupin turned very quickly.