Tracking Down

There was a layer of dust on the screw's surface, but a small ring around its edge showed signs of wear, as though it had come into contact with some kind of tool.

The wear was very recent, and the surrounding dust had not yet covered it.

"Someone definitely tampered with the hinges. They might not have picked the lock, but they tried to open this door some other way."

The three of them walked along the fourth-floor corridor to the stairwell. Hermione stopped. "If he is interested in the fourth-floor corridor, he will probably come back. We do not need to wait here the whole time, but we can leave a marker—trap a hair or a thin thread in the crack of the door. If the door has been opened, the marker will shift."

"Let's use a hair." Harry plucked a hair from his head, walked to the abandoned bathroom door, and wedged it into the gap at about the middle of the frame, where it would neither be easily seen nor naturally fall out.

After securing the hair, he stepped back to the stairwell and looked at it.

Unless someone leaned in for a close look, they would never spot that hair.

"If someone opens the door, the hair will either fall to the floor or get caught on the other side of the gap," Hermione said. "We'll check again next morning."

That afternoon, they went to Hogsmeade as planned. Pabbie picked out several bags of spices at the seasoning shop, Seamus found two more old books at the Second-hand Bookshop, and Pansy stood before the shelves leafing through books for a while. She bought nothing, but noted down several titles.

Ron bought that bag of peppermint, opened it, and tried one. Nodding, he said it really was