Disclaimer: Still don't own Life with Derek.

Author's Note: In case you haven't seen "Grade A Cheater" yet, Casey and Derek are not nearly as out of character in this chapter as you might think. Casey really is pretty bad at math and Derek does pretty well at it when he bothers to put in the least bit of effort.

Chapter #5--Up in Arms

Casey was in the hall, talking to Tinker. She was hoping that he might be able help her understand the latest math lecture. Math had always been Casey's weakest subject and since they had moved on from derivatives to integrals in Calculus, she found it particularly challenging.

Tinker was always glad when Casey asked for his help, although frankly, he wasn't sure why she didn't just ask her stepbrother. Derek had been getting better and better at math since he had started to apply himself more.

"So if the integral of 2x is x-squared plus C," she was asking, "how do I know wha—"

Casey words came to a halt when she felt a pair of arms slung around her waist.

"Der-ek!" she yelled, not even needing to turn around to see whose arms they were.

Tinker saw an amused smirk form on Derek Venturi's face.

"You can't find C," Derek said, anticipating her question, "unless you're given more info. Because the derivative of a constant is always zero."

"Um, actually that's right," said a flustered Tinker.

"My brains are one of the many reasons Casey wants me," Derek said, addressing Tinker, who seemed increasingly uncomfortable.

"In your dreams, Derek," said Casey. "After all, you're the one with your arms around me."

"It's charity," said Derek, not batting an eyelash, nor, as Tinker observed, bothering to remove his arms. "You know you can't get enough of it."

"Don't be ridiculous," retorted Casey, "you're the one who I always hear saying my name though the wall at night."

Tinker also noticed that Casey wasn't bothering to push his arms off her and that Derek's face had turned slightly pink.

"Yeah," he responded, as if her words had not affected him in the least, "on the phone, complaining about your annoying crush on me."

Casey seemed to be getting more and more angry.

"Um, maybe we should go over this later, Casey," Tinker said.

"Sure, Tinker, thanks for all your help," she said.

Tinker noticed that she hadn't commented on the fact that her stepbrother had started to move one of his thumbs across her stomach.

Tinker got out of there as fast as he could. If he'd ever had a chance with Casey McDonald, he knew that he didn't anymore.

"That," Derek whispered, leaning into Casey's ear, "was for Virginia Hamilton."

Casey smirked. She had purposely embarrassed him in front of some girl he had been chatting up in the hall yesterday.

"Well," she said to him, "turns out it doesn't bother me in the least."

"It . . . It doesn't?" he asked her, getting a happy goofy look on his face.

"No," she said, frostily, finally pushing his arms off her and turning around to face him. "Because unlike you, I don't want to jump into bed with every person of the opposite sex that I talk to."

With that she turned around, and walked away from him down the hall.

"Yeah," he yelled loudly with an air of cockiness in his voice, "you just want to jump into bed with me!"

Casey gave a nervous laugh to a group of people who seemed to be watching her and continued down the hall.

Derek would have to pay for that, she thought.