The oaken door swung open, and -

Harry didn't bother to stop himself from screaming as he threw himself backwards and away from the triplicate sets of glinting teeth. He landed, not hard enough to hurt a wizard, and drew his wand and roared "Stupefy! Stupefy!"

The first stunbolt dazed the creature slightly, but before the second hit home a chunk of Hogwarts' stone wrenched itself free of the floor and flew into the path of the spell. The levitation visibly left it just before the bolt hit, and then it melded back into the floor.

"Not bad as a reaction, Mr. Potter," said Professor Quirrell's somehow-audible voice over the creature's many-voiced roar, "but consider that Dumbledore designed this chamber as a game for eleven-year-olds." A genuine-looking smile. "Before he ever saw an army of them. This creature, which our intrepid groundskeeper informs me is named Fluffy, is Charmed to spit students out without harming them. Now, how do you suggest we deal with this most terrifying of creatures?"

"Ah," Harry said as he tried to slow his heartbeat down, "if, um, Fluffy is like Cerberus in Greek mythology, because that phrase is not ridiculous at all, then we could sing to it?"

Professor Quirrell was giving him a look.

The Killing Curse is unblockable, unstoppable, and works every single time on everything with a brain.

"Um. We might trigger alarms by going in all wands blazing?"

"That was a flimsy excuse, but very well."

A flick of the Defence Professor's wand, a sound like a hundred songs played backwards in the space of a second, and Fluffy collapsed in a snoring heap.

"As for alarms, Mr. Potter," said Professor Quirrell, "the race between magical defence and offence is a decisive win for offence, which is why modern cursebreakers can pierce the tombs of ancient wizards, and so I confess myself impressed that Dumbledore's wards took me many months to untangle." He gestured Harry forwards. "After you."

Harry entered the chamber before his brain caught up with him, and he turned to behold a more-evil-than-usual smirk. Harry swallowed, trying not to imagine what his parents would say.

The room was high and dim, lit only by small, high windows set into recessed alcoves. The stone was grey and coarse, cemented together roughly, more like a ruined Muggle fortress than the rest of the castle Hogwarts. "Lumos," Harry muttered, focussing the light into a narrow beam like a torch, and began to inspect the featureless alcoves.

"What are you doing, Mr. Potter?"

"Searching the room. There could be some sort of inscription, or a key we'll need later, or a hidden passageway, or-"

Professor Quirrell massaged his temples briefly. "As it happens, your mastery of Muggle role-playing games might serve you well if you ever feel the urge to enter the Tomb of Amon-Set, but I remind you once again that Dumbledore built this game, this false puzzle, for first-years."

"Ah."

Harry skirted the drooling Cerberus and eased open the worn trapdoor, which disappointingly failed to creak eerily.

The pit dropped far below, he couldn't tell how far but it looked a long way below ground level, insofar as that meant anything in Hogwarts. He thought he caught a glimpse of something wriggling at the very bottom.

"Broomstick" said Harry to his pouch, and he climbed on and gestured Professor Quirrell towards the back seat.

Professor Quirrell floated gently into the air.

Harry noticed his confusion. "I thought wizards couldn't levitate themselves?"

"Quite so. It is said to be like lifting oneself up by one's own bootstraps. And indeed, one of the Dark Lord's most feared feats was to fly like smoke on the wind, unsupported but for his own wizardry. How did he and I do this, boy? Answer as quickly as you can."

I'm sorry, are we really still buying that he isn't Voldemort? asked Slytherin.

He swore he wasn't, in Parseltongue, spoke Ravenclaw, although admittedly it still probably isn't a good idea to trust him. So what do we know that has the power to fly?

"Um... you cast broomstick enchantments... no, you had someone else cast broomstick enchantments on your underwear, then Obliviated them."

"Cloth would not hold the magic. Broomstick enchantments must be cast on a long, narrow, rigid shape."

Perhaps Harry had been spending too much time around the older Ravenclaws, because he had to fight down a snicker at that. "How long does it have to be? Could you just strap short broomsticks to your arms?"

"Indeed, I did at first. And yet..." Professor Quirrell rolled up his sleeve to reveal a bare, wasted arm.

Harry raised an eyebrow. "You have broomstick enchantments on your bones?"

"And in thirty seconds of creativity, Mr. Potter, you have solved what has been called one of the greatest challenges of modern wizardry." A shake of the head. "Even after much study of the Muggle arts of psychology and some curious Legilimency, I have yet to discover just what is wrong with ordinary people, that they do not seek to optimise what they see. If only the lore of the legendary Felix Felicis were not lost to the ages... but I digress."

Professor Quirrell flew neatly down into the pit, and Harry followed.

Carefully avoiding a patch of what Harry recognised as Devil's Snare, they came to another stone chamber. The air was filled with a metallic rustling, and hundreds of multicoloured birdlike keys fluttered about the ceiling. The light from the enchanted windows, unbroken stained glass panes that stretched from floor to ceiling, was rosy and soft for all that they were underground, and the winged keys scattered rainbow spots over the smooth bright stone.

"Excuse me, but this just violates every possible rule of security. If you think you've secured a door with a lock, you keep the key safe and give it only to authorised entrants, you don't give the key wings and leave a broomstick propped against the wall. I know this place was made for first-years, but did that really not occur to anyone who came through here?"

"Perhaps you ought to give the Legion further lessons, General Chaos."

"Hmph. So how are we going to go through this one?"

"I assume you never tried out for Ravenclaw Seeker, Mr. Potter- it really is rather disconcerting to be glared at like that by an eleven-year-old. Well, as you insist."

The Professor drew his wand and touched it to his breast. With a drop of blood clinging to the end of his wand, he traced in the air a flaming rune, all jagged edges and malevolence, looking disturbingly wrong. Harry took a step back.

"Az-reth, az-reth, az-reth."

Twisting flames poured out from the rune, redder than blood and haloed in yellow-white and shot through with further black than midnight. The fire burned too brightly for its wine-dark shade of red, glared like the setting sun just as it touches the horizon, not quite unbearable to look at. The fire formed the shapes of dragons and lions and snakes, and they began to multiply and expand to fill the room. The heat blurred Harry's vision and crisped his hair. Sweat dripped from his forehead, but an icy chill ran up his spine. His dark side, or just plain instinct, was urging him to stay well away from the cursed fire.

Harry's Inner Ravenclaw suggested that the reason it looked so wrong was simple: in everyday experience, hot objects didn't usually glow that brightly in that shade of red due to the way black-body radiation behaved.

That explanation offered little comfort.

When Professor Quirrell locked eyes upon the Fiendfyre, it turned in on itself and shrank, taking the shape of a foul black-burning phoenix.

And something told Harry with burning certainty that if that balefire phoenix met Fawkes, the true phoenix would die and never be reborn.

The door burst into flames even before the false phoenix reached it; with a single sweep of its molten wings, the door vanished in a white flash, and the red-rimed doorway dripped stone. Professor Quirrell drifted sedately after the flames, the stone freezing in place as he passed.

Harry tried to turn to his dark side, which prompted a sudden thought. Only mostly Voldemort... His dark side, clearly, was the remaining influence of Lord Voldemort on his mind, thinking habits and feelings somehow leftover from imprinted memories that shouldn't have still existed.

Harry probably ought to have been more worried about turning out to be somehow partly the Dark Lord, but frankly that sounded a lot like something the hero agonised over for years, before finally realising that it was his choices that made him who he really was and that he obviously wasn't as evil as Voldemort.

Now that he knew what his dark side was, Harry thought he should be able to call on the icy calmness without falling into the less desirable parts of the pattern.

An ever-so-slightly cold Harry stepped over the threshold.

The vast chamber was torchlit this time. A few steps in front of Harry started a huge chessboard of black and white marble squares, each two metres or more on each side, stretching from wall to distant wall. Chess pieces almost the size of Hagrid stood on the board, intricately carven of granite, looking for all the world like well-made statues.

The room was high enough for the ceiling to be far out of reach of the statues.

Harry was about to suggest that the obvious solution was to simply fly over the board when he noticed that some of the pieces carried bows.

Professor Quirrell glanced at the board, and the black king and queen turned and stepped aside.

"Well," spoke Professor Quirrell, "since we still have four and a half hours until you leave the Quidditch game, it seems that we can afford to play. I am sure you are positively bursting with questions, and have done an admirable job keeping quiet. Take the king's place, and I shall take the queen's. Let us play, and I shall answer your questions if you have them."