Accept the twins' help.

Fred and George each grab one of your arms, and lead you into a disused classroom on the ground floor. When they let go of your arms, you sink down to the floor, your hands, which have definitely not turned blue, covering your eyes. Your head starts pounding, and your skin feels like it's burning. You give a loud shout, and in a moment, Fred and George are kneeling next to you. They grab you, but pull away straight away.

"You're burning hot", Fred said, worried.

You barely hear him. There is a loud ringing in your ears, and your skull feels like it's about to explode. You let out a long groan. In the corner of your mind, the part that isn't occupied with the agony you're in, you can hear Fred and George discussing your condition with worry, but can't concentrate enough to take in the words. It's just easier for you to sit there, and hope that the pain goes away quickly. The ache in your head increases, becoming overwhelming. You squeeze your eyes tight shut, but, if anything, this makes it worse. Slowly, your mind goes blank.

You slowly rise up from the darkness, to find yourself staring up into the faces of Fred and George. When they see your open eyes, they smile in relief

"What happened?" you try to say, but only a croak comes out.

You try to sit up, but can't move any part of your body more than a few centimetres before you're tired out.

"Let us help you", says Fred, anxiously.

The twins kneel on either side of you, and prop you up against the teacher's desk in the front of the room. The feeling of cool hands of naked skin makes you gasp, and you realise that you are naked. You try to ask a question, but again, are only able to bring Fred and George's attention to you. Luckily, George is able to decipher your incoherent rasps.

"Your clothes just burnt off", he said, the shadows in his eyes hinting at the fear he must have felt. "We couldn't get near you, you were that hot."

"The potion didn't turn your skin blue, at least", Fred adds. "Though it caused other changes."

Fred's eyes flicker down your body, then away. Rousing all your energy, you tilt your head to look down. Just as George said, you're naked, but that isn't what makes your eyes widen in surprise. Your cock, which normally is average size, around 15 centimetres when fully hard, is now around 20 centimetres, and it's still flaccid. You can only imagine how big it will be when it's hard.

"When your clothes burnt away, your cock began to grow", continues Fred, his face turning the same colour as his hair, as a blush creeps up his cheek. "It seems to be… um… an interesting side effect."

All this talk of your cock makes the subject of the conversation stir. While you're unable to do more than tilt your head, and make a crude semblance of speech, your cock has no such restrictions. Blood pumps from all across your body down to your crotch, and you stare as your cock grows past 25 centimetres. You can feel the gazes of Fred and George on you, or, to be more accurate, on your cock, as with each heartbeat, your cock throbs, and grows ever larger. Finally, it reaches its final length – a whopping 35 centimetres long. To you, it looks more like a third leg, then a cock, but Fred and George think otherwise.

"It's so big", George says, his voice raw.

You turn your head slightly to look at the redhead, and see awe in his face, and something else, possibly hunger. A touch on your chest makes you flinch, but you quickly realise that it's only Fred's hand. Fred traces a pattern down your chest, his fingers following the trail of hair that leads from your belly button to your cock. His hand then grips your cock. You flinch again, and try to knock Fred's hand away, but you still don't have the strength.

"My hand can't even go around his whole cock", Fred said in wonder.

"This definitely is an interesting side effect", George added. "If we could get rid of this weakness that Harry has, this potion may be good for our sex aids line."

You try to protest at the twins' handling of you. You don't like how that talk as if you can't hear them, and act like you're just an experiment. But again, you manage only a squeak before your voice gives way. By now, George has also grabbed your cock, and together the twins stroke it. The stimulation sends bolts of pleasure throughout your body. It seems that the potion not only made your cock larger, but also more sensitive. As if the twins can sense your pleasure, they speed up their ministrations. Finally, when your whole body is tingling from the pleasure, your cock suddenly shoots jet after jet of cum into the air. Fred and George stare as your cum reaches the second row of desks that face the teacher's table. You close your eyes, more exhausted than ever, and hope that your cock will revert to its normal size. While you don't mind the size and sensitivity at the moment, you can see how it could be difficult in everyday situations.

But your cock doesn't shrink back to its normal size. It doesn't even soften. After a few minutes, you feel a tentative touch on your cock. Your eyes fly open to see George run his finger from the head of your cock to your base. Cumming has made your cock even more sensitive than before. A line of fire follows George's finger down your cock. You try to scream, but your throat still refuses to cooperate with you.

"He's still hard", George muses, gripping your cock once more.

The fire that blossoms at his George's touch returns, but this time, it is joined by new tendrils of pleasure that make you giddy. While George occupied himself with masturbating your cock again, Fred reaches underneath to fondle your balls. You moan loudly, to Fred and George's amusement. Your eyes close, and you surrender to the pleasure.

When you open your eyes again, you're unsure how much time has passed. You notice that while you were occupied with your feelings, Fred and George have undressed, and while both are still playing with your engorged cock, they are also jerking off as well. That sight, of the redhead twins getting off to your cock is enough to push you over the edge. Your orgasm comes as a surprise to Fred and George, and they both get splattered with your cum. Nonetheless, neither Fred, nor George stop masturbating, and shortly, they cum, within seconds of each other, their eyes still locked on your cock. The three of you sit in the classroom for a while, exhausted. Finally, you realise that your cock has shrunk back to its normal size.

"Thanks", you say, your voice raspy. "That was great. I should test your potions more often."