Harry Potter and the Half-Blood Prince

He set off around the edge of the lake, and Harry followed close behind him. Their footsteps made echoing, slapping sounds on the narrow rim of rock that surrounded the water. On and on they walked, but the view did not vary: on one side of them, the rough cavern wall, on the other, the boundless expanse of smooth, glassy blackness, in the very middle of which was that mysterious greenish glow. Harry found the place and the silence oppressive, unnerving.

“Professor?” he said finally. “Do you think the Horcrux is here?”

“Oh yes,” said Dumbledore. “Yes, I’m sure it is. The question is, how do we get to it?”

“We couldn’t… we couldn’t just try a Summoning Charm?” Harry said, sure that it was a stupid suggestion. But he was much keener than he was prepared to admit on getting out of this place as soon as possible.

“Certainly we could,” said Dumbledore, stopping so suddenly that Harry almost walked into him. “Why don’t you do it?”

“Me? Oh… okay…” Harry had not expected this, but cleared his throat and said loudly, wand aloft, “Accio Horcrux!”

With a noise like an explosion, something very large and pale erupted out of the dark water some twenty feet away; before Harry could see what it was, it had vanished again with a crashing splash that made great, deep ripples on the mirrored surface. Harry leapt backward in shock and hit the wall; his heart was still thundering as he turned to Dumbledore.

“What was that?”

“Something, I think, that is ready to respond should we attempt to seize the Horcrux.”

Harry looked back at the water. The surface of the lake was once more shining black glass: The ripples had vanished unnaturally fast; Harry’s heart, however, was still pounding.

“Did you think that would happen, sir?”

“I thought something would happen if we made an obvious attempt to get our hands on the Horcrux. That was a very good idea, Harry; much the simplest way of finding out what we are facing.”

“But we don’t know what the thing was,” said Harry, looking at the sinisterly smooth water.

“What the things are, you mean,” said Dumbledore. “I doubt very much that there is only one of them. Shall we walk on?”

“Professor?”

“Yes, Harry?”

“Do you think we’re going to have to go into the lake?”

“Into it? Only if we are very unfortunate.”

“You don’t think the Horcrux is at the bottom?”

“Oh no… I think the Horcrux is in the middle.”

And Dumbledore pointed toward the misty green light in the center of the lake.

“So we’re going to have to cross the lake to get to it?”

“Yes, I think so.”

Harry did not say anything. His thoughts were all of water monsters, of giant serpents, of demons, kelpies, and sprites…

“Aha,” said Dumbledore, and he stopped again; this time, Harry really did walk into him; for a moment he toppled on the edge of the dark water, and Dumbledore’s uninjured hand closed tightly around his upper arm, pulling him back. “So sorry, Harry, I should have given warning. Stand back against the wall, please; I think I have found the place.”

Harry had no idea what Dumbledore meant; this patch of dark bank was exactly like every other bit as far as he could tell, but Dumbledore seemed to have detected something special about it. This time he was running his hand, not over the rocky wall, but through the thin air, as though expecting to find and grip something invisible.

“Oho,” said Dumbledore happily, seconds later. His hand had closed in midair upon something Harry could not see. Dumbledore moved closer to the water; Harry watched nervously as the tips of Dumbledore’s buckled shoes found the utmost edge of the rock rim. Keeping his hand clenched in midair, Dumbledore raised his wand with the other and tapped his fist with the point.

Immediately a thick coppery green chain appeared out of thin air, extending from the depths of the water into Dumbledore’s clenched hand. Dumbledore tapped the chain, which began to slide through his fist like a snake, coiling itself on the ground with a clinking sound that echoed noisily off the rocky walls, pulling something from the depths of the black water. Harry gasped as the ghostly prow of a tiny boat broke the surface, glowing as green as the chain, and floated, with barely a ripple, toward the place on the bank where Harry and Dumbledore stood.

“How did you know that was there?” Harry asked in astonishment.

“Magic always leaves traces,” said Dumbledore, as the boat hit the bank with a gentle bump, “sometimes very distinctive traces. I taught Tom Riddle. I know his style.”

“Is… is this boat safe?”

“Oh yes, I think so. Voldemort needed to create a means to cross the lake without attracting the wrath of those creatures he had placed within it in case he ever wanted to visit or remove his Horcrux.”

“So the things in the water won’t do anything to us if we cross in Voldemort’s boat?”

“I think we must resign ourselves to the fact that they will, at some point, realize we are not Lord Voldemort. Thus far, however, we have done well. They have allowed us to raise the boat.”