The Sorcerer's Stone could end the War before it even began.
With it in his possession, Voldemort would be permanently immortal, and the word of what amazing power the Dark Lord had would spread quickly, convincing more and more people to join his cause, them too frightened of being on the losing side to do anything else. With his ranks swelled, he could catch Dumbledore unprepared, storm Hogwarts and the Ministry, conquer the Wizarding World in one swift blow.
He could be a king, and Harry could be a prince.
And then, he could do anything he wanted. Sentence Weasley to have his soul sucked out by Dementors. Feed Hagrid to one of his pets. Lock McGonagall in a room with some Pitbulls while she was in her cat form. Cruciatus Mrs. Norris to death.
And those were only the first four he could think of off the top of his head. And oh, did he ever feel satisfied just imagining them.
But, then again, he wouldn't be able to do any of that if he were dead.
"—but then he won't see you as an asset any longer. He'll see you as a threat. He'll kill you."
Harry didn't want to believe Grindelwald. He wanted to think that, while his father was evil, he still cared about his own son, that he wasn't inhuman enough to just throw away a child he'd raised from infancy.
But he would be lying to himself. People feared Voldemort for a reason, people called him the darkest wizard ever to live for a reason. Harry didn't understand a lot of what he did, the evil he committed, but he didn't want to, because sometimes he was afraid that if he ever started to understand a twisted mind he'd become twisted himself, and that was something he hoped would never happen, because insanity scared him more than anything. His mind was the one thing he had total control over, and to lose even that was something he didn't want to contemplate.
However, the threat of death seemed a bit more imminent, and so he found it more pressing an issue.
He could give his father the Stone, that little red Stone that even now sat in his bag, wetting his robes with immortal water.
And then—
—"Father," he'd say, smiling a sly little smile and holding the Stone behind his back. "You'll just never believe what I've gotten for you."
He'd reveal it, Voldemort would smile a wide, genuine smile, one like he'd never seen before, and hug him and say, "I'm so proud of you, son!" and they'd live happily ever after like something out of a fairy tale, father and son, king and prince—
—or—
—Voldemort would smile a wide, nasty smile, take the Stone, draw his wand, and Harry's life would end in a flash of green light and the words "Avada Kedavra!" and Voldemort would only ever say, "You've served your purpose" to his corpse.—
Sickly sweetness and total coldness. Two extremes. Couldn't he imagine anything in between?
No, he answered a moment later, because Voldemort was always extreme, no matter what he did. He couldn't just dislike Muggles, he had to start a war over it. He couldn't just resent his father, he had to murder him. Voldemort was never in between.
"Are you okay?" asked Hermione, looking at him and frowning. She sat across from him, next to Neville, and looked a bit concerned.
Harry cleared his throat. "Fine. Just a little headache. Keep talking."
She nodded slowly, and Neville resumed his story.
"Well, there's not that much more to tell, but—I bounced! It was the magic! Everyone was so relieved!"
Draco was staring at him. "They threw you out a window? And off a pier? Did they want you to die? Should you even be going back to these people?"
Neville was still smiling. "It was the proudest day of my life, other than getting my Hogwarts letter. I would've been so ashamed if I were a squib. Did anybody else do any accidental magic?"
"Once I made flowers bloom in my mum's garden during January," said Hermione, grinning fondly at the memory. "My grandparents were staying over for the New Years and they didn't know what to make of it, but my parents had known there was something strange about me since I made my older sister's skin turn green for an entire day when she stole my Miss Daisy doll."
Draco stared at her.
"I was four years old, okay?" she snapped, only to turn around and look at him pointedly.
He smirked. "I set a House Elf's hair on fire."
"House Elves have hair?" demanded Neville.
"Some," said Draco. He sneered. "You'd know if your family could afford them."
"Are you sure you didn't use a match?" asked Hermione skeptically.
He sniffed. "Of course I'm sure. Harry was there!"
Silence. He glared. "Right, Harry?"
"Hmm?" Harry looked up. "Oh, yeah, House Elf. Hair on fire. We were five, you were mad because he brought you the wrong kind of chocolate from the kitchen and bam, flames. Never did grow back, the poor thing. What was his name? Demmy?"
"Dobby."
"Right. And then once your mother had put it out he insisted on hitting himself on the head with a lamp to apologize for making you upset."
Hermione cringed. "They actually do that? I mean, I'd heard they practiced self mortification, but I'd thought that that was a long time ago—"
"No," said Draco. "They still do it today. Old habits, and all that. Once I saw one slam a door on its own ear. Repeatedly."
Neville looked a bit ill, and everyone independently decided to stop talking.
Harry looked back down at his lap, not caring if anyone noticed how subdued he was. For a moment, he almost wished the Stone had been destroyed, that he could just go home and enjoy his summer.
But, he thought, looking out the window, it was going to be a dark, wet summer, anyway. And his father didn't need the Stone, not now. The War hadn't begun, his plans weren't fully formed, and he didn't seem to be in any danger of dying.
And besides, perhaps Harry didn't want to share. He needed everything he could get for a future he was unsure of.
So, he'd simply save it for a rainy day. Daddy didn't have to know.