She she has a good reason for sneaking into Justins' room, she really does. He might argue, but in her mind it's a good reason. She also has a good reason for snapping photos with her phone. She's going to blackmail him with all the weird stuff in his room, and it's going to be awesome.
She's pretty much having the time of her life, rummaging through his stuff, taking photos of all the dumb stuff he has lying around, it's like her birthday, only she doesn't have permission this time, which makes it all the more fun, plus she has an excuse to practice the invisibility spell, which she is so using right now.
"Yeah, just a second, Max, I need to get something" she freezes, Justin's coming! No, scratch that, he's already here. She thinks for a moment that she can sneak out through the breifly open door. Until he closes it, and she realises all hope is lost. And then she remembers she's invisible and hits herself on the head, or at least she tries too, but she knows it'll make a noise, so she stops short of her forehead.
She figures she can live until Justin leaves, she just has to be careful and avoid him bumping into hurt, he's moving around the room pretty fast though, and he seems to be angry.
"Alex was in here! She moved everything too! I'm going to kill her!" he grumbled unhappily, cleaning things up. He's throwing some things into their appropriate general areas, and Alex is having a hard time avoiding them, it's almost like he knows where she is. The thought crosses her mind, but she's pretty sure Justin can't see the invisible... Can he?
He suddenly trips on something and crashes into a table that happens to have a bottle on liquid on it, the bottle breaks and the liquid spills onto his shirt and pants, Alex tries really, really hard not to start laughing.
He gives an angry distorted groan. Alex moves away from him quickly and hides in the alcove of his room, well, she's not really hiding, but she's pretty sure he won't come over here.
And then it happens, and Alex really wishes it hadn't. Justin looks at his shirt and then begins to pull it over his head. Alex really wishes she wasn't staring, and that Justins' body hadn't gotten so... manly... She's blushing. She doesn't mean too, his chest just looks so amazing, she'd blush if she saw it on any guy, really, she would.
His finger hooks into the waistband of his pants and her breath catches in her throat, her eyes widen like saucers and she lets out a small squeak when she realises what he's about to do. And then he stops, and starts looking around frantically and she realises she made a noise and now she wants to hit herself really, really hard because she's an idiot... But he was about to take his pants off and she really didn't want to see that. … Well, she doesn't think she did, but for a moment she's a little upset that he's stopped, the thought disgusts her and she pretends it was never there.
He suddenly begins to walk towards her and she doesn't think she's ever been so scared. He knows she's there, he knows, he so knows. She closes her eyes and then peeks one open to check if he's still there. He is. And his handing is reaching out to her, this in itself isn't quite as scary as where it's reaching. She looks behind her and realises she's in front of a book shelf, and her right breast happens to be just in front of a book on laundry. She rolls her eyes, Justin is by the far the biggest geek alive. But his hand is about to touch her breast, her brother is about to accidentally grope her. There are just so many things wrong with that.
She thinks on her feet and moves out of the way quickly, it's an awkward angle though, but he grabs the book instead of grabbing her breast, so even though her arms are now in the air, she's on her tip toes and her back is arched over and she's right in front of another shelf which happens to have heavy trophies on it, she considers it a victory. Until she lets out a sigh of relief, and which point Justin drops the book because now he knows he isn't alone. He starts looking around, and his arm accidentally hits Alex on the back and she crashes into the trophy shelf and is now trying to catch the trophies that keep trying to crush her. Meanwhile, Justin has grabbed his wand, and turned her visible, and now he's just staring because she's not wearing any clothes and wow, did she always look this good?
She turns to him, realises he's staring, looks down and figures out that she's now visible... and naked. … She drops the trophies and they just stare at each other, looking the other over thoroughly. And then Alex glares at him.
"How come I'm completely naked and you're only missing a shirt?" she demands.
"Because I didn't sneak into my brothers room!" he throws back. She smirks.
"Well, I can fix that" she says, walking towards him and he realises she's not talking about sneaking into Maxs' room, he blushes heavily and backs away from her, only that's not as easy as he wants it to be, because she's backed him into a wall and she's still coming towards him. Before he can openly protest, she attacks him with a kiss and she doesn't think she's ever enjoyed being caught so much. And judging by the thing that's now pressing into her exposed thigh, she doesn't think he's ever enjoyed catching her so much.

I would write more, but I'd rather not go too far into M territory. Make your own conclusions about what just happened.
I wonder if I switched tenses during this story? I'm sure there are spelling mistakes... Whatever.
Written because I snuck into my own brothers room earlier (he stole my iPod Shuffle, I wanted it back) and while I was moping about being caught because he came home early, I wished I had magic powers so I could be invisible, and then... yeah, I eventually got to this. ^-^; Well, hope you liked it, read, review, enjoy.

(This is the first time I've written something that isn't so overwhelmingly angsty, hooray~! I totally had to throw logic out the window to do that though, oh well, logic makes incest bad, logic sucks D:)