This story began as a result of a conversation at The Teachers' Lounge about what would have happened if Ron, rather than Harry, had been on the chamber side when the ceiling of the passage below the lake fell in. It is dedicated to the denizens of the Lounge.

Ron, Tom Riddle, the Basilisk and anything else you recognise, belong to JKR, and the first paragraph is lifted in its entirety from Harry Potter and the Chamber of Secrets, with one very significant change of name.

Our Sister's Keeper

The wand Lockhart was holding exploded with the force of a small bomb. Ron flung his arms over his head and ran, slipping over the coils of snakeskin, out of the way of great chunks of tunnel ceiling which were thundering to the floor. Next moment, he was standing alone, gazing at a wall of broken rock.

"Harry!" he yelled. "Harry! Where are you? Are you okay?"

"Yeah, I think so," came Harry's voice. "Lockhart's not though. Dunno what your wand did to him, but he doesn't look very with it."

Ron surveyed the rock wall in front of him. It looked horribly solid. "D'you think we can get through this?" he asked doubtfully.

"I've got my wand still," said Harry. "I'll see if I can shift some of it with that. Don't want to bring the whole ceiling down though. I don't know how long it will take…"

He sounded strangely hesitant, as if waiting for Ron to say something.

"I'd better go on," Ron said, trying to sound braver than he felt. "Someone needs to get to Ginny soon."

"Yeah," Harry said, sounding relieved. Ron wondered if he'd been waiting for him to volunteer to go on alone. He needn't have worried, he thought a bit grumpily. Ginny was his sister, after all.

"I'll go then," he said. "See you later."

"Good luck!" Harry called. "I'll join you as soon as I get through this lot."

Which might take a while, Ron thought, as he turned and headed down the dark passageway he found himself in. For now, he was on his own, and wandless.

The passage went straight for a while, then turned left, right, then right again. Abruptly, Ron found himself in front of a sheer stone wall adorned with two serpents, their eyes glittering jewels. There didn't seem any way in. What the hell should he do now?

Look for the weak point. Bill's voice was in his head, as calm as it had been when he had been teaching a five-year-old Ron to play wizard chess. There's always a weak point somewhere.

Ron scanned the apparently sheer wall in front of him, and sure enough, there was a very faint line zigzagging down it. A door then. But how to get in? He scanned the wall again – no sign of a keyhole. A password?

"Alohomora!" he cried, wishing he had a wand in his hand. No harm in trying the obvious first. "Open! Open up!"

Know your enemy, little brother. This time it was George's voice in his head, and Ron could see him grinning maliciously at his goalkeeping failure as Fred did a lap of honour around the apple tree they were using as a Quidditch goal. Know your enemy.

Know your enemy. Slytherin. Slytherin was a Parselmouth. The password would be in Parseltongue. He turned and ran back along the passageway at full pelt, skidding to a halt at the wall of rock. From the other side, he could hear the grate of stone on stone as Harry struggled to clear a way through.

"Harry!" he yelled. "Harry!"

"Ron?" The stone-moving noises stopped abruptly. "Have you got her? Have you got Ginny already?"

"No!" Ron cried, struggling for breath after his run. "I can't get through. Harry, how do you say 'open' in Parseltongue?"

"What? Oh. Open." Harry said.

"English," Ron snapped impatiently. "I need the Parseltongue. Concentrate, that's my sister in there!"

There was a pause, and then Harry made a hissing, spitting sound, which Ron tried to copy.

"No good," Harry said. "Try again. Listen." The hissing sound was repeated, and again Ron tried to copy it.

"That was 'package'," Harry said, sounding impatient. "Listen."

Again he made the hissing sound, and again Ron tried to copy him.

"Rabbit," Harry said, sounding increasingly agitated. "Try again."

Again he made the noise, and again Ron tried to replicate it. On the sixth attempt, Harry gave a low cheer.

"That's it! That's it! Just do it like that, and you'll be fine."

"Okay," Ron said, sounding a lot more confident than he felt, and he set off at a run again along the passageway, repeating the odd hissing sound he had learnt over and over in his head as he ran.

Back at the serpent-adorned wall, he opened his mouth and made the hissing sound as well as he could. Nothing happened. Again and again he tried, with no result, until he was nearly frantic. His little sister was in there, and he was the only person who could rescue her, and here he was shouting "Package!" and "Rabbit!" uselessly at an apparently impenetrable wall.

Calm down. It was Bill again.

Ron tried. He took several deep breaths, and then tried the hissing again. This time it worked. The wall parted along the almost-invisible crack and he was facing a huge towering chamber with twisted columns reaching up higher than he could see, each one with a stone serpent coiled around it. He started to run forward, opened his mouth to shout his sister's name.

Careful. This time it was Charlie. Snakes can feel vibrations through the ground. Take it slow.

Ron gulped and headed forwards slowly, hardly daring to lift his feet from the floor. The chamber loomed above him, dark and mysterious. He wished he had a wand – even his Spellotaped broken wand would be better than nothing. He was straining his ears for any sound that might be the Basilisk, but the chamber was silent. Then he saw her, at the foot of an enormous statue that must be Salazar Slytherin himself, Ginny, lying in a crumpled heap of red hair and black robes either asleep or…

Despite Charlie-in-his-head, Ron called out his sister's name and ran forwards, dropping to his knees beside her and shaking her by the shoulders. Her eyes were closed and she was chalk white, but she was still breathing.

"Ginny! Ginny, wake up, we need to get out of here!" Ron urged her desperately, but her head lolled back and she showed no sign at all of having heard him. Ron swallowed hard and tried to think what to do. Perhaps if he could get her onto his back, he could carry her - she was pretty light after all. Mind made up, he squatted down in front of her and managed to pull her arms over his shoulders. Standing up, he realised that this was going to be nowhere near as easy as giving her a piggy back while she was awake and alert. She was a dead weight on his back, and he doubted he could manage to get her out. Still, he had to try.

"Put her down!" The voice was cold and hard and peremptory. Ron jumped, but continued to cling to Ginny's cold hands. Opposite them stood a dark-haired boy who appeared to be about sixteen. He was regarding Ron coldly. "Put her down!" he repeated. "Who are you, anyway?"

Ron let his sister slide down gently to the ground. "Who are you?" he demanded, trying to sound braver than he felt. "Can you help me? I need to get my sister out of here. There's a Basilisk. It could come at any moment." He looked around nervously, but there was nothing moving, no one there but himself and Ginny and the dark-haired boy.

There was something very odd about the boy. He seemed not quite solid. He moved forward, smiling nastily.

"Oh, so she's your sister, is she, poor little Ginny?" he asked. "Poor poor little Ginny. She says her brothers tease her." He looked at Ron accusingly. "Do you tease her?" he asked.

"Yes, sometimes," said Ron, surprised into answering honestly. "But what the hell's it got to do with you? How do you know, anyway? Who are you? Why won't you help us?"

His questions were becoming more and more frantic, but the boy just continued to smile and to look at him with disdain.

"Help you? Blood traitors and Mudblood lovers?" he asked coolly. "Why ever would I do that? Your bones will lie here with your fool of a sister's, a lesson to anyone who dares oppose me, the Heir of Slytherin!" He opened his mouth again and made a hissing sound. Almost at once, Ron heard something moving overhead, something huge, something terrible. Above them, he could see movement, and then a vast snakelike body crashed down on the floor of the chamber in front of where they stood. The strange boy was laughing, still making the hissing noises. Ron ran.

Ron narrowed his eyes as much as he could and still see, dodging between the pillars, hearing an awful slithering sound behind him. It was fast. The boy was laughing, and urging the beast on in his strange hissing language.

"You see, little blood traitor? You see what happens to any who dare challenge the greatest wizard of our day?"

Ron was behind a pillar, bent over and gasping for breath. This time it was his father who spoke in his head. Albus Dumbledore is the greatest wizard of our time.

Ron straightened up. "You aren't!" he yelled defiantly. "Dumbledore's the greatest wizard alive today! No one even knows who you are!" Then he began running again. The huge snake slithered behind him. It was getting closer.

The boy laughed nastily. "Oh, you know who I am, little blood traitor. You know my name, though you are afraid to say it. I am Lord Voldemort, powerful enough to be brought back from a memory in a diary by an eleven-year-old girl of no family and no talent."

"I don't believe you!" Ron shouted, even as he realised it must be true. It made sense that You-Know-Who should be the Heir of Slytherin – though how this boy, who was only a few years older than he was himself, could be Voldemort was beyond him.

The boy was hissing louder now, apparently urging the Basilisk on. "It's true," he said. "You know it is. Who else could be the Heir of Slytherin, the greatest and truest of the Hogwarts Four? I am Lord Voldemort and I am so much more powerful than your Albus Dumbledore can ever hope to be. He was driven from Hogwarts by my mere presence."

Father says that Dumbledore was the only person You-Know-Who was ever frightened of. Ron had never been so grateful for one of Percy's pompous pronouncements.

"Rubbish!" he cried, skittering to a halt behind a pillar and leaning against it while he gasped for breath. "Dumbledore's better than you! You're scared of Dumbledore!" How he managed to inject such scorn in his voice when he could scarcely breathe from both exertion and terror he didn't know, but somehow he managed it.

The hissing started again, and he took off running as the huge snake moved behind him. But there was another sound now. Music was coming from somewhere, and the flutter of wings. Ron tripped and fell hard, rolling over and screwing his eyes shut, waiting for his inevitable end. A weight fell in his lap, soft but heavy, and above him he could hear the basilisk making a high hissing sound. Something wet dripped onto his arm. He opened his eyes and risked a look upwards. There was a bird, yellow and golden and red, fluttering around the head of the giant snake. One huge eye was dripping blood, and as Ron watched, the bird jabbed at the other with its beak and blood spattered the stone walls above the Basilisk's head.

Not any old bird, little brother, that's a Phoenix. Charlie's voice was admiring, maybe even a little envious.

"Nothing to be envious of here," Ron thought grimly, because the Basilisk was on the move again. Could snakes smell their prey? It seemed like it; the creature seemed to be heading straight for him. The bird – Phoenix – gave a high keening cry and disappeared upwards and away. Ron pulled himself to his feet, looking down in confusion at the bundle he was holding. His confusion increased as he realised it was the Sorting Hat. But there was something inside – Ron put his hand in and pulled it out – a long silver sword, adorned with glittering rubies.

Not just any sword – that's the sword of Godric Gryffindor. Now it was Bill's turn to sound envious.

(This was ridiculous. If he ever got out of this, Ron was going to have serious words with his brothers. Surely it wasn't normal to have members of your family popping up in your head like this in moments of stress.)

The Basilisk was on the move again, its sightless head bearing down on where Ron stood. Without really thinking about it, he grasped the hilt of Gryffindor's sword with both hands and thrust it upwards with all his might. Blood drenched him, sticky and cold. With seconds to spare, he crouched and rolled to the side as the great Basilisk crashed to the ground where he had been standing and was still at last.

Pulling out the sword from the great snake's neck and scooping up the Sorting Hat, Ron ran back to where his sister lay. There was no sign of the strange boy – of You-Know-Who. Was it his imagination, or did Ginny seem even paler than before? And was her breathing shallower? Dropping the sword and the Hat on the floor, Ron crouched to pick her up again. His hand touched something firm lying on the ground underneath her robes and he pulled it out – the battered old diary he had seen Harry with, and which had shown Harry the story of Hagrid and the boy Tom Riddle. Harry had said Tom Riddle was dark-haired. Could he be You-Know-Who? Ron shook his head in frustration. None of this made any sense. He would worry about it once he and Ginny were safely out of here.

"Leave her!" The boy – You-Know-Who – was back, and he had a wand pointed straight at Ron's chest. Ron recognised it as Ginny's. "Leave her alone! You may have beaten the Basilisk but you will never beat me! The greatest wizard of all time cannot be defeated by a pair of blood traitor children. You will both die here!"

Ron shuffled backwards, trying to shield Ginny's body with his own. They were going to die. Despite everything, despite the miracle of the Phoenix and the sword and the dead Basilisk, they were going to die. The sword! Ron's scrabbling hand reached it and he lifted it high in front of him – the boy that was Voldemort was laughing, enjoying his moment of triumph.

"You can't fight a wand with a sword, idiot boy!" he cried. But Ron did not turn the sword on him. Instead he brought it hard down beside him where Tom Riddle's old diary lay.

There was a scream and Ginny's wand clattered to the floor, ink poured in torrents from the diary, soaking Ron and Ginny's robes and covering Ron's blood-spattered hands. The boy was fading, collapsing in on himself, disappearing before Ron's eyes. And Ginny was stirring, colour returning to her face. She pulled herself into a sitting position and looked at Ron confusedly.

"Ron? How did you get here? Where's Tom?" And then, as Ron put his arms around her and pulled her into a hug, she began to cry.

He pulled Ginny to her feet as the sound of running feet heralded Harry's arrival.

"Ron? Ginny? Are you okay?" he asked breathlessly. "What happened?"

Ron scooped up Ginny's wand, the Sorting Hat and Gryffindor's sword from where they lay. Harry's eyes opened wide at the sight of the Hat and the sword.

"What happened?" he repeated.

Ron laughed and began to lead the way towards the chamber entrance, one arm still around Ginny's shoulders.

"It's a long story," he said. "But I'm not telling it here. Let's get out of this place."

There was a squawk and the Phoenix reappeared, flying down from the heights of the chamber to lead them to freedom. Harry's eyes opened still wider.

"I can't wait," he said weakly.