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"Expecto Patronum," whispered Harry.
And just like that, effortlessly, gracefully, a silver stag stepped from the end of his wand, turning its misty silver eyes towards him.
"Why have you summoned me?" it seemed to ask. "I have no purpose here. There are no enemies to fight, no darkness to battle."
Harry shrugged. "I dunno," he murmured, almost to himself, stretching out a hand to the wispy shape. "I guess I just wanted to feel... well... not so alone."
And the Patronus dipped its silver head in quiet understanding, and stood silently before him. But as soon as his hand touched the shining mist, the shape swirled and dissolved into nothingness, leaving only a vague feeling of peace and happiness.
And Harry knew he could confide in his Patronus, because it would never tell anyone (how could it, anyway?) his deepest fears and secrets.
The next time Harry summoned his Patronus, a hundred dementors were closing in on him, but it was another Harry, a different Harry. And he watched as the stag proudly galloped around the lake, scattering dementors on all sides, and finally trotted back.
"Prongs," he whispered, and reached out a trembling hand -
But then the moment was gone, the peace and calm were gone, and only a race against time remained, to save Sirius and get back to the hospital wing, and Harry would not meet his Patronus again for some time.
Four months later, silver hooves danced soundlessly across the stone floor as Prongs emerged.
"Hi, Prongs," said Harry.
Prongs did a funny little jiggle, as if he was saying 'Hi' back.
"You don't mind if I talk to you, do you? I mean... I know you're not really alive, but-"
Prongs tossed his misty silver head and stamped silently.
"I thought it would be different," said Harry softly. "At primary school, everyone hated me. I thought it would be different here."
Prongs stopped, and stepped closer to Harry, tilting his head like a curious child, and yet his silver eyes were full of wisdom.
"I guess I was wrong," Harry whispered with a sad smile.
Prongs stepped closer, and the warmth and joy washed over him like hot sunshine after a cold, snowy night. 'It's all right,' the ethereal stag seemed to say. 'Even though the world is unpredictable and fickle, you only have to call for me, and I'll be here.'
And Prongs filled up some of the hole in Harry's heart, that had appeared when Ron had turned away.
Whenever Harry was feeling down, Prongs was there to cheer him up.
And Harry knew that Prongs was just a spell, he wasn't real, wasn't really sentinent, wasn't really his friend, and he shouldn't get attached.
But he was always there, waiting, ready to come with just two words-
"Expecto Patronum."
And he would never abandon him, because he was him, a part of him.
All the time he would have spent with Ron, he now spent with Prongs, the ghostly silver stag that spoke without needing words, and walked on air like a graceful swan.
And Prongs understood him, understood like no-one else ever could, because he was him, and Harry was Prongs, and they were one, really.
But still, Harry liked to think of Prongs as someone else-
Just so he didn't feel so alone.
"Hey Prongs." Harry smiled as the familiar wave of happiness and contentment washed through him. "I survived a dragon! And Ron and I are friends again!"
The Patronus pranced in circles around him, a reflection of his own jubilant mood.
"I had an idea, Prongs," continued Harry, grinning. "Want to play?"
And he whispered, "Aguamenti," and a gentle stream of water appeared, Prongs prancing and frolicking in the showers of rainbow dewdrops, shining as the sunlight streaming down.
And in that moment, nothing could go wrong, nothing mattered, not the rules, not the sky, not his friends, nothing mattered except Prongs, and his beautiful, graceful, lithe figure, dancing in the wind and the sun.
And Harry laughed, laughed out loud, like he hadn't since the days when he lived in blissful, infantile ignorance, and another Prongs, a solid Prongs, was dancing in front of him in a small cottage in Godric's Hollow.
Before the second task, the Goblet spat out the name of the person that Harry would miss the most. And it was Harry Potter. It was Prongs, really, but Prongs was a part of Harry; he was Harry. So the judges took Ron instead.
"Expecto Patronum!" yelled Harry.
Prongs seemed to give him and amused look, before turning and cantering towards the dementor. And it stumbled, and then Harry knew it wasn't a dementor, not really.
"Prongs... Please stay with me?" Harry whispered to his guardian.
The Patronus bowed his great antlered head, and the two set off into the darkness of the maze together, the stag unseen by any but those he wished.
"Avada kedavra!"
Prongs leaped into the path of the curse, head held high, its sickly green light shining greatly at odds with his gentle silver, and disappeared.
The light carried on, deadly green, and a tall, blonde boy fell to the ground.
And it was shameful, but all Harry could think about was Prongs, and whether he would come back, as his wand was wrenched away and he was bound to a cold marble headstone in the dark graveyard.
He didn't speak.
He watched numbly as a tall, pale, thin man (was he even a man anymore?) stepped out of the cauldron.
And Cedric Diggory did not emerge from Voldemort's wand.
Harry ran towards the cup, dodging spells that flashed around him like fireworks, threw himself over Cedric's still-breathing body, and-
"Accio cup!"
Harry said nothing. He sat in Dumbledore's office, paintings staring, little trinkets puffing, Dumbledore's questions flying over his head like wind over the ground, and shook his head mutely, eyes vacant.
He lay in the hospital wing, silently listening to Dumbledore and Fudge arguing.
He stood in a deserted corridor, mustering up the courage to cast the spell again.
He wouldn't know what to do if Prongs didn't appear...
He would be lost.
"Expecto Patronum."
It came out in a wavering whisper, unsure and trembling.
Nothing.
No, thought Harry in disbelief. No! It can't be happening!
"Expecto Patronum!" he shouted desperately. Again and again. Despair filled his mind. Prongs would not come back.
He thought of his friends, Hermione and Ron, and Sirius, and Mrs Weasley's hug in the hospital wing.
"Expecto Patronum," he whispered, one last time.
And Prongs burst forth from the tip of his wand in a blaze of silver glory, and Harry barely registered that the hooves clattered and the head tossed with a woosh, because all that mattered was that Prongs was back-
And as he turned, Harry leaped at him and threw his arms around the silver neck - the solid silver neck - and sobbed in relief.