Some twisting of the canon timeline was involved here, but I had to have the Boggart Scene. I have done some paraphrasing and quoting from The Prisoner of Azkaban (disclaimer: the book belongs to JKR, not me, even though I've got some Beef with the author), but please don't skip that scene because I've made a considerable change to the outcome.
Content warning: Harry's relationship with the Dursleys, as well as their effect on his mindset, are the main topics of this chapter.
Spotting Peeves coming right for them, Yellow ducked and pulled Green with him. The poltergeist, who was busy clawing at his nose and swearing up and down the rainbow, didn't take notice of the boys and continued down the hall.
"Thanks," Green said faintly, staring at something over his shoulder. Yellow followed his surprised gaze to see Peeves hovering at the end of the hall and violently blowing his nose. One particularly emphatic honk sent the poltergeist spinning halfway around. Yellow snorted and had to clap his hands over his mouth to suppress a giggle.
"Is that…gum up his nose?" Blue asked. "I guess he really can be corporeal."
"Now's not the time to make up words, mate!" Red cried, sprinting past the rest of the group. "Our class is getting away!"
Indeed, their class was filing out of the Defense room and following Professor Lupin to another classroom. The Harrys, running as quietly as possible to avoid drawing the professor's attention, joined the crowd. Blue immediately started worming his way to the front of the group. Yellow followed after him with a small sigh. He might have been too short to see over everyone's heads, but he knew Hermione was likely right behind Professor Lupin. As fixated as Blue was on the Hogwarts Bestiary, Yellow didn't doubt the boy would start some Drama (with a capital "D") to get it back, even if the professor were right in front of him.
Sure enough, once he came upon the bushy-haired bookworm, Blue hissed, "Hermione, give it—!"
Yellow gripped his shoulder and tugged him into a half-hug. "You can ask her nicely once we get back to Gryffindor Tower," he hissed into Blue's ear. He matched the suspicious look Hermione was shooting Blue with a sunny smile. "Silly Blue forgot we were in class," he explained to her in a low voice. "Where are we going, anyway? Are we having a field trip?"
"The professor just said we were having a practical lesson. Wands only," Hermione replied. "If it involves Cornish pixies, I'm ready for it."
Professor Lupin led them to a long room with worn, wood-paneled walls and mismatched chairs scattered about. Most of the furniture had been shoved against the walls, clearing a path to the one remarkable object in the room.
A shabby wardrobe sat near the back wall. Yellow found the lack of chairs and tables around it peculiar until the wardrobe violently rattled. He squeaked in surprise and ducked behind Blue. What was trapped inside it, an angry Moblin?!
"It's perfectly safe," Professor Lupin assured his startled class. "There's a boggart in there."
Ron got a funny look on his face, as though he found the two statements paradoxical. A number of other students—Neville in particular—stared at the professor like he'd said something utterly mad.
"Though one would assume otherwise, the boggart isn't trying to get out," Professor Lupin told them. "They like dark, tight spaces like wardrobes, rarely-opened cabinets, underneath beds—I've even come across one that made its home in a grandfather clock." He walked up to the wardrobe, completely at ease, and put a hand on its side. "A boggart decided to move in yesterday afternoon, and I made a request to let my third-years have a go at it before the Headmaster banished it."
"Why would you do that?" Neville asked in a tiny whimper.
"So, do any of you know what a boggart is?" Professor Lupin asked, having not heard (or deciding to ignore) Neville's question. "I understand that their definition can be a slippery one."
Hermione and Blue fought to be the first to put up their hands. Blue even stood on tiptoe to put his higher than Hermione's, a stubborn pout on his face. When Professor Lupin called on him instead of Hermione, he shot the girl a triumphant grin before declaring, "A boggart is a shape-shifter that takes the form of one's greatest fear. It changes shape the moment anyone looks at it, so no one knows whether it has a natural form."
"Couldn't have put it better myself," Professor Lupin said with a nod. "The boggart will assume the form most terrifying to the person looking at it. This gives us the advantage." His tired brown eyes flicked over the crowd of anxious third-years. "Green, could you hazard a guess why?"
Green looked startled. He glanced at Blue and Hermione, who had their hands in the air, before stammering, "Er, because there are so many people looking at it? It'll get confused, right?"
"Exactly," the teacher replied. "When dealing with a boggart, always bring a friend. Not only is it practical, but it can have entertaining results. When the boggart gets confused, it has no idea what to turn into…"
A dark flicker caught Yellow's eye, distracting him from Professor Lupin's ongoing lecture. He scanned the back left corner of the room, which was somehow unlit by the magical light that evenly illuminated the rest of the space. Shadows clung unnaturally to the scuffed wooden panels and threadbare rug. He squinted suspiciously at them. Hmm.
"…You see, the thing that really finishes a boggart is laughter," the professor was saying. Yellow focused back on Professor Lupin, though he watched the shadows out of the corner of his eye. "What you need to do is force it to assume a shape you can laugh at. We'll practice the charm without wands first, so you get a feel for it." Lupin raised his hand as though it held an imaginary wand, and his class did the same. "After me, please…Riddikulus!"
"Riddikulus!" the students parroted.
"Yes, that's it. Now comes the more difficult part. Now for someone to start us off…Aha!" The professor beckoned to Neville. "Here is where you come in, Neville."
The boy stepped forward. He looked as though he wanted to protest, but was too scared to make his mouth work. Yellow was tempted to run up and hug him. Poor Neville really needed one.
Neville wobbled toward the wardrobe, his face the color of cottage cheese.
"Now that you're here, Neville, what would you say is your greatest fear?" Lupin asked.
Neville made a squeaky noise, like a deflating balloon.
A spark of mischief lit up the professor's faded brown eyes. "Sorry, didn't catch that," he said cheerily.
Looking as though he dearly wished a Floormaster would rise from the dusty carpet and whisk him away, Neville whispered, "Professor Snape."
There were only a few giggles. Had the Gryffindors not seen Snape after Neville's Keese-infused potion had gone off like a stick of dynamite, more of them might have laughed. Neville's pinched features relaxed by a millimeter or so.
Professor Lupin had taken Neville's confession in stride and appeared thoughtful. "You live with your grandmother, don't you?" he asked.
"Yes?" Neville said slowly, clearly wondering what this had to do with anything. "I'd rather the boggart didn't turn into her, either."
"No, no, that's not what I meant." Professor Lupin wore a smile reminiscent of the Weasley twins'. "Could you tell us what your grandmother usually wears?"
"Well, er…"
A movement in the shadows drew Yellow's attention away again. What was that? If it had been a Keese, it would have fluttered out and started diving at people already. Whatever was hiding there, it was patient. He drilled the shadows with his gaze while Professor Lupin talked Neville through how he would deal with the boggart. Something was watching them, and he wanted to know what.
A pair of yellow eyes, uncannily similar to his own, appeared in the shadows. He gasped and jerked back just as the doors of the wardrobe opened with a loud bang.
Yellow found himself dragged backward by a hand on his shoulder as Snape stalked out of the wardrobe and toward a trembling Neville. The professor looked like he had after his classroom had been spectacularly blown up, his face contorted in rage and his robes billowing like storm clouds.
Neville retreated a few steps, shaking harder than ever, as the false Snape swooped down on him. After four steps, he seemed to brace himself and then stammered, "R-R-Riddikulus!"
With a loud, sharp "crack!" Snape stumbled. His intimidating black robes had been replaced by a lace-trimmed dress the color of pea soup. Upon his greasy locks sat a peculiar hat featuring a stuffed vulture, and an oversized crimson handbag now swung from his wrist.
Yellow was too unsettled to join in the laughter prompted by the boggart's unintentional transformation. While Professor Lupin called up the next student, he turned to see who had pulled him safely away from the boggart.
Concerned brown eyes stared back at him. "You okay, Harry?" Ron asked. "I saw you get spooked by something before Lupin opened the wardrobe. What was it?"
"Er, it was…" Yellow noticed that the strange film of shadows had peeled away from the wall, leaving nothing unusual to show it had ever been there. "I'll tell you later," he said. No point in worrying his friend now, especially when they were fighting a monster that was only vulnerable to laughter.
Seamus was currently up, fighting a banshee. The creature opened her mouth, filling the room with a painful inhuman shriek, not unlike that of a ReDead. Her wail was cut off when Seamus's spell made her go hoarse.
"Have you thought about what you're most afraid of?" Ron asked as they watched Dean catch his greatest fear—a severed hand—in a mousetrap. "You already know mine. It's spiders."
"I don't know," Yellow admitted. There were a lot of things he was afraid of. Voldemort was one, though that fear had lessened since the battle at the end of first year. The basilisk was another, though the horrible snake was thankfully dead. Then there was the Dementor…
He shuddered, imagining the creature's rotting, slimy hands and tattered cloak. Like it was a corpse still wrapped in a death shroud...He remembered an aura of death and despair, the screams echoing in his ears as the ability to breathe escaped him—
But there weren't any more Dementors guarding the school, were there? He hadn't even seen them floating around beyond the barrier that encased Hogwarts. Was he even likely to see another one of those things, given that they usually guarded Azkaban? As often as Snape, Filch, and his relatives insisted he was a troublemaker, he was no criminal-to-be.
Alright, Dementors were possibly out of the running, then. What did he have a deep, dedicated fear of like Ron did with spiders? He honestly couldn't think of anything.
Ron was called up, and the boggart became a spider as tall as Snape. Bristling with spiky hair, the Acromantula advanced on Ron. Venom oozed from its long fangs, an acid green fluid that hissed when it dripped on the floor. Ron looked up at it with wide, terrified eyes. He wasn't the only one; several students had pressed themselves against the walls, as far as they could get from the beast. After several seconds of standing frozen, Ron leveled his wand at the spider and roared, "Riddikulus!"
The spider's legs vanished and it hit the ground with enough force to send a tremor through it. Disoriented, the boggart began rolling around erratically. Lavender, who had surprisingly not fled from the spider along with most everyone else, screamed and leapt out of the way before the limbless arachnid could bowl her over.
Yellow edged back as the boggart came for him and sighed in relief when it stopped at his feet. In his peripheral vision, he saw Professor Lupin lunge for it. He frowned in confusion as he readied his wand. What was the professor so worried about?
Before Professor Lupin could get between Yellow and the shape-shifter, the boggart changed forms with the sound of a whip-crack. A bristling moustache and purpling, puffy cheeks replaced the spider's fangs and pedipalps. Uncle Vernon stood in front of him, larger than life. Tremors shook Yellow's slight frame as he looked up and up and up, his eyes taking in the meaty fists and sausage-like fingers, huge arms, and expression of nail-spitting rage. He felt like a five-year-old who'd committed the unspeakable crime of sneaking a chicken leg from the fridge.
He didn't want to get locked in the cupboard again!
Yellow backed away, knowing from years of experience that he had to get out of reach before he started pleading. "U-Uncle Vernon, I'm s-sorry—"
"Yellow!" Hermione's worried shout snapped the boy out of his terrified trance.
Boggart! He was facing a boggart, not his uncle. Muggles couldn't even see Hogwarts, and a man like Uncle Vernon wouldn't have come within a kilometer of the place even if it weren't hidden under an illusion.
Now realizing the true situation, Yellow scrambled for an idea before the boggart made a move for him. What was funny? How could he make Uncle Vernon funny?
The mustache quivering under the boggart's nose gave him an idea. "Riddikulus!" he shouted. There was another whip-crack, and then a very confused walrus sat where Uncle Vernon had previously stood.
"Very good, Harry!" Lupin called. Yellow noticed that the man looked more frazzled than usual. "Neville, finish it off!"
Neville rushed forward, his wand at the ready and his round face set with determination. "Riddikulus!" Neville cried. Snape appeared for a split-second, dressed in Lady Longbottom's eclectic wardrobe, before Neville barked out a laugh. The boggart exploded into a thousand wisps of silvery smoke that then faded to nothing.
The class breathed a relieved sigh and then burst into applause. Students broke away from the walls and congregated around Neville, some of them clapping him on the back.
"Excellent work, everyone!" exclaimed, Professor Lupin. "Especially you, Neville. Very well done. Now, as for points…five to Gryffindor for each person who faced their fears—ten to Neville for doing it twice—and five to Harry Potters Blue and Green."
Yellow couldn't bring himself to feel happy about getting points. He could only see Uncle Vernon's plum-colored face and balled fists. All of the other Harrys were going to be furious with him—he knew it. No one was supposed to know about how the Dursleys acted toward him. Every time he'd tried to tell someone about it, the Dursleys had made him out to be a liar and then treated him even worse. He'd just condemned himself and his brothers to a summer of hell!
"Thank you for that wonderful demonstration, all of you. For homework, I'd like you to read the chapter on boggarts and summarize it to be handed in on Monday. That will be all…" He motioned to Yellow before the boy turned toward the door. "…except for you. May I have a word with you, Yellow?"
A sudden urge to cry seized Yellow. He bit down hard on his lower lip. Everything was ruined and it was his fault!
"What did you want to want to talk about?" a more confident version of his voice asked. Yellow looked up, a hopeful smile forming on his lips at the sight of Red standing with him. The other Harrys were there as well—Blue with his hands on his hips and Green wearing a serious frown.
Professor Lupin didn't object to the presence of the other Harrys. "It occurs to me that I know nothing of your home situation," he remarked.
"Dumbledore said that was to protect me from Voldemort," Green said shortly. He crossed his arms. "Why do you want to know about it?"
"Your brother's greatest fear is a man he called 'Uncle Vernon'," Professor Lupin said. It sounded like a condemnation to Yellow's ears. He'd failed to keep the big secret.
Red looped an arm around Yellow and pulled him close. Yellow leaned in, feeling stupid for acting like a little kid but comforted all the same.
"He's big and loud, and he's always been that way. He scared us when we were younger," Blue said with a forced shrug. "So what?"
"You're thirteen, not a small child, and he's what Yellow fears most," said the professor. "I find that telling."
Uh-oh. Now Lupin sounded like the school nurse who'd found bruises under Harry's sleeve. A week later, she'd been fired and Harry had been locked up in the cupboard from Friday afternoon to Monday morning with only two bathroom breaks and one piece of bread a day. That had gone on for four weekends, until Uncle Vernon and Aunt Petunia had found something else to punish him for.
"I'm just a 'fraidy cat!" Yellow burst out. "Ask any of us! It's the other three who got all our confidence, not me."
"Yellow, you saw Neville's boggart, didn't you?" Professor Lupin asked kindly. "Would you say that his fear is unfounded, or that he's just a ''fraidy cat'?"
"Well…no, 'cause that would be mean and Snape is actually kinda scary. Especially to Neville," Yellow mumbled. "He almost poisoned Neville's toad today in Potions. He was going to feed Neville's potion to Trevor even if it was messed up."
A dark expression crossed Professor Lupin's face before it was replaced by a gentle smile of encouragement. "See? He has a legitimate reason to be afraid of Professor Snape. I believe you have a very real reason to be afraid of your uncle, beyond a mere lack of confidence."
"If you look into this, you'd better not tell the Dursleys," Red said. "You'll get us into trouble, and you aren't the one who has to spend the summer with them."
Professor Lupin frowned. "…I see. Well, then, I'll be discreet."
Ron was feeling very left out of the loop. He'd had this vaguely unpleasant sense for a little while now—since Harry had been split into four, in fact. While he knew there were times when he could come off as thick, he could be observant when he was motivated to be. The four Harrys were keeping the same secret that the original Harry had been keeping since Ron had met him; the only difference was that the multiple Harrys had a habit of speaking their internal monologue aloud.
Since first year, Ron had known Harry didn't get along with his family. Harry never mentioned them, for one thing. If anyone brought them up, Harry was quick to change the subject. There had been signs pointing toward mutual dislike over the years—a toothpick for Christmas here, an offhand comment there. The most memorable of these was the set of bars that had been over Harry's window when he and his brothers had rescued him from Privet Drive in their father's flying car. Why would the Dursleys have put bars over Harry's window? He'd never really thought about it before, but it was kind of scary when he stopped to consider the implications; he and the twins had gone there to rescue Harry from boredom, but had they been saving him from more than that?
And now there was a new, even more disturbing sign: Yellow's boggart. He'd been shocked to see the same unpleasant, mustachioed man whom he'd seen picking up Harry from the train station at the end of the school year. The boggart's version of him had been over two meters tall, his face an unnatural shade of plum and his fists oversized, but he'd been recognizable as the same man. Even more, Yellow had actually called him "Uncle Vernon".
Why was Yellow so scared of his uncle? Ron couldn't fathom being afraid of a member of his family. Families loved each other, didn't they? Not even the most unpleasant of his relatives, with their habits of drunkenly railing about politics or going on at length about how great his older brothers were, came close to frightening him.
Harry and Yellow walked into the dorm room, speaking to one another in lowered voices and snickering. Upon seeing Ron, Harry explained, "Blue's trying to get into the girls' dorm to steal the Bestiary back. Red's standing at the bottom of the stairs to laugh at him."
Had he been any less consumed with worry, Ron would have gladly gone to watch Blue's futile struggles. As it was, though, he put on a Hermione-like frown and asked, "Are you okay, Harry?"
The two Harrys gave him identical confused looks. "Yeah. The boggart didn't hurt us, and those Octoroks that ambushed us during Care of Magical Creatures got squashed by Hagrid before we could get hit," the green-eyed one said.
"I didn't know you could slay monsters by stomping on their heads! I wish we were big enough to do that," Yellow mused wistfully. "I bet Dog could do it if he wanted. He's a big boy."
Ron's frown almost broke into a smile, but he held it together. "No, it's not about that. I was wondering why your boggart looked like your uncle."
The atmosphere of the room suddenly went cold. "Professor Lupin already interrogated us about this," Harry said flatly. "It was nothing. Yellow just had a scary nightmare about Uncle Vernon a little while ago and the boggart picked up on it. It's not something you need to worry about."
"One nightmare doesn't turn your uncle into the absolute scariest thing you can think of," Ron argued. "I mean, I've had a couple of nightmares about gnomes dragging me into their burrows, but my boggart didn't turn into one of those. You're scared of your uncle. Why? What did he do to you?"
Harry crossed his arms and kept his lips firmly pressed together. Yellow, on the other hand, looked like the truth was going to come leaping from his mouth whether or not he wanted it to. The boy bounced on the balls of his feet and refused to make eye contact with Ron or Harry. He bit his lower lip hard, putting his hand to his mouth every few seconds like he was tempted to hold it shut.
"I-I…" Yellow screwed his eyes shut. "I saw Shadow Harry in Defense Class!" he burst out. "He was watching us! I don't know why, but he was hiding in the corner!"
The non-sequitur derailed Ron's train of thought. "What? Shadow Harry?" Ron asked dumbly. "Yellow, what're you talking about? What's this got to do with—?"
"Shadow Harry? You mean that bloke who showed up after I pulled the sword out?" Harry asked.
Ron attempted to get things back on track. "Harry, that's not what—"
"Yeah, it was him," Yellow said. He glanced guiltily toward Ron. "I saw his eyes—like mine, but glowy and kind of greenish."
"Have you seen anything like that before?" Harry inquired. "Do you know if that's the first time he's spied on us?"
"If he's done it before, I didn't spot him," Yellow said. Edging toward the door, he asked, "Er, shouldn't we tell Red and Blue? And Hermione?"
"Yes, definitely." Harry hooked his arm around Yellow and then hustled them both out of the room.
Ron was left staring at the departing boys' backs. 'What's wrong, Harry? Why won't you tell me?' he thought sadly. 'Aren't I your best friend?'
Just in case anyone gets the idea that Harry's behavior is something I would endorse: no, Harry is not having a healthy reaction toward others' expressions of concern. He's just so used to being punished every time he tells someone what his home life is like that he avoids offers of help like the plague.