Unfortunately for Harry, Priori Incantatem doesn't exist.
A jet of green light issued from Voldemort's wand just as a jet of red light blasted from Harry's — they met in midair — the red spell was flung aside, shattering a nearby headstone with a bang. Harry however didn't have time to flinch, as his vision was filled with a green light, his ears hearing nothing but a great rushing sound.
Harry Potter fell, in good company among the dead.
Slowly, consciousness began to return to Harry. He slowly realized that he was indeed 'there', that he wasn't just a wisp of vapor from a forgotten thought.
He lay facedown, listening to the silence. He was perfectly alone. Nobody was watching. Nobody else was there. He was not perfectly sure that he was there himself.
Time passed, or maybe it didn't. Lying down was a strange sensation for someone who moments before had believed he was not a physical being. He was naked, but he found he didn't care. It was strange enough to drum his fingers on the ground, the sensation of touch so exciting with each soundless tap.
Whatever he was lying on was neither hot or cold, it was simply there. Harry then realized he had eyes, so he opened them.
White. A vapor-like mist that seemed to form vague shapes and patterns. He looked around as he sat up. It was as if Harry was in a massive building shaped by clouds. The floor was white too, but that wasn't mist, it was hard and solid, like a pain of glass that had been frosted over.
He jumped slightly as a groan rang out, breaking the complete silence. He had been certain that he was alone. He glanced around him, suddenly conscious about his nudity. As his thought materialized, robes appeared feet from him. He quickly pulled them on, not surprised that they were warm and soft.
Harry walked through the mist, following the groans. It danced around his body as he strode through it. As a child, Harry had imagined walking on the clouds that appeared on bright sunny days, he imagined walking on clouds, if it were possible, would be like this.
He reached where the groans came from. It was the only thing aside from the robes that Harry'd seen that wasn't white. The noises came from what looked like a small, naked child. It was a repulsive sight, Harry took in its' flaying skin, its' too thin frame. It was curled up underneath a seat, as if it had tried to hide from something or someone.
"You can't help it," called a familiar voice.
Cedric Diggory stood feet away, Harry couldn't figure out where he'd come from. He too was dressed in robes, but while Harry's were black Cedric's were a brilliant shade of yellow.
"What is it?" Harry questioned.
"A lost soul," Cedric replied, rather unhelpfully.
Harry was nonplussed by that answer, but then realized where he'd last seen Cedric. He forgot about the creature. "Are we dead Cedric?" Harry asked, recalling the events at the graveyard.
"I am," replied Cedric, seemingly not fussed by this statement.
"Then … I suppose I'm dead too?"
"Actually," said Cedric, "that's a bit more complicated."
It wasn't much of an answer, but it seemed like Cedric thought it was one as he turned and began walking away from Harry. Harry quickly followed, not wanting to be left alone with whatever that whimpering child was. Cedric strode confidently through the mist, over to a pair of seats that Harry hadn't noticed before, perhaps they hadn't been there he mused. Cedric sat down, and waved Harry into the seat opposite him. Harry sat.
"So?" Harry prompted, looking Cedric in the eye.
"You're not quite dead," Cedric said.
"But I was hit with a killing curse, Cedric." Harry knew His hand went to his scar, or where it should have been. He couldn't feel it. "I died."
"You did die Harry, so did I. But You-Know-Who made a mistake," Cedric smiled. "He took your blood."
Harry had no idea what that had to do with anything. "And?"
"And in your blood, Harry is the reason why you survived the killing curse all those years ago, do you remember the reason why Quirrel couldn't touch you."
Harry's brain began to whirl. He recalled in his first year after Quirrell had tried to kill him, the conversation with Dumbledore. His mind could recall the memory with utter clarity. It was, Harry thought, probably how Hermione's brain worked all the time.
"Voldemort wanted my blood for that reason, he wanted the protection my mother had died to give me."
"But that's not how this kind of magic works Harry," said Cedric. "He didn't steal your mother's protection, not in the way he intended. It won't work for him that way."
"When You-Know-Who took your blood he also took your mother's protection, he unknowingly tied his fate to yours. Your mother's sacrifice now resides in you both, he gave you a lifeline."
"So I'm not dead?" questioned Harry.
"You are and you aren't, time as a concept doesn't apply here," Cedric replied.
That wasn't much of an answer, Harry thought, but Cedric didn't seem to be in the mood to provide any. He figured it was probably about as good a reply as he was going to get. "Where is here?" Harry asked as he looked around. Moments before, he was sure he would have had no answer. Now he did.
"Why does it look like King's Cross Station?"
"King's Cross!" Cedric laughed. "I suppose that makes enough sense."
"What? Where are we really?" Asked a bemused Harry.
"Oh I have no idea Harry, this is your … Er … Station I suppose."
"My Station" Harry repeated.
Cedric smiled. "And you have the very rare choice of deciding to board a train or go back."
"A train to where?" asked Harry
"On," Said Cedric, with a terrible finality.
Harry was confused. "How do you know all this, about Quirrell and blood magic and the like?"
"Time as a concept doesn't apply here," Cedric repeated. "And there's plenty of reading material that has kept me busy. I had a… I'm not sure how to describe it, a precognition I suppose. I knew you'd arrive here eventually, and that you'd be given a choice."
Harry glanced around. Maybe that's why Cedric had laughed, maybe instead of King's Cross he saw a vast library, Hogwart's library perhaps.
"If I go back, I'll be alone against Voldemort and his Death Eaters."
Cedric flinched at the mention of Voldemort, and the whimpering child let out a low groan. "You'd have a chance, not a great one but you'd have one. Your summoning charm is pretty impressive, and I doubt they've thought about deactivating that portkey."
Harry remembered the pain of the Cruciatus Curse, how it had felt like every bone had been burning, his skin peeling, his scar erupting. He didn't want to experience that again.
"I would have one request," Cedric started, looking hesitant for the first time. "Could you bring my body back? Bring me back to my parents. Give them something to bury."
"But why would I go back?" Harry questioned. "I don't know magic strong enough to fight off Voldemort, I won't survive anyway."
"Even if they're not expecting me to get up after the curse, they're still surrounding me. I'm outnumbered Cedric, horribly outnumbered. I can't fight that many adult wizards, I'm not Dumbledore." Even Dumbledore couldn't fight that many death eaters and Voldemort at the same time Harry reasoned. "I'm just not powerful enough, there's no point."
"Besides, I've lived thirteen years when I should have died as a baby. That's a good life, it's a good amount of extra time. I've already had a second chance."
"You're only fourteen Harry, you've not lived yet!" Cedric looked shaken now. "I can't believe you'd even consider going on, what about your friends? What about your family?"
Harry refrained from laughing at the thought of the Dursley's mourning him, but it was a near thing. "My family will probably throw a party, they don't care about me. And my friends have families of their own Cedric, they'll be fine."
"My family is dead Cedric, I'd like to see them again."
"What do you think Voldemort will do to our bodies Harry? Have you heard of Inferi?"
"No? Are they magical creatures?"
"Not even close, Harry. They're reanimated corpses, it's a form of Dark, Dark magic. It's like making a corpse into a mindless puppet. How do you think our friends and families will react when Voldemort sends our corpses to attack them?"
Harry felt sick. "Reminated- that's horrible."
"I don't want to be Voldemort's puppet Harry, please."
Well, there wasn't much Harry could say to that. He imagined his own corpse, one hand on Ron's throat and the other on Hermione's.
"How do I go back then?" Harry asked, resigned.
The mist had begun to thicken. "You're already on your way," Cedric replied.
"What!" Squawked Harry, indigent. Bright light encompassed his vision as he heard Cedric laughing.