“Hermione – what’ll happen – if we don’t get back inside – before Dumbledore locks the door?” Harry panted.
“I don’t want to think about it!” Hermione moaned, checking her watch again. “One minute!”
They had reached the end of the corridor with the hospital wing entrance. “Okay – I can hear Dumbledore,” said Hermione tensely. “Come on, Harry!”
They crept along the corridor. The door opened. Dumbledore’s back appeared.
“I am going to lock you in,” they heard him saying. “It is five minutes to midnight. Miss Granger, three turns should do it. Good luck.”
Dumbledore backed out of the room, closed the door, and took out his wand to magically lock it. Panicking, Harry and Hermione ran forward. Dumbledore looked up, and a wide smile appeared under the long silver mustache. “Well?” he said quietly.
– Joanne K. Rowling, Harry Potter and the Prisoner of Azkaban