A/N: I never do this! I never write one-shots between stories because I really don't know if I'm good at them, but this idea kept me up at night so I might as well make it count.

On a side note, when I try to write drabbles I always end up making them longer than intended. At least it's not 'To Err is Human' long.

Also this is my first try at present tense. And my first try at humor and friendship in a while. I tried. He-he.

Hope you like it!

Disclaimer: Turtles and Casey are not mine!

Basic Trig

Casey Jones' gloved fingers tap his forearm in an unsteady rhythm. His mind clouds with sudden indecision. But ultimately he strides into the workshop. He doesn't know what to expect, but a warm welcome is certainly not his first guess. Which is good, because Donatello is not giving one. In fact, the stickmaster extraordinaire is showing Casey his shell and is lost on whatever project that rests on his desktop. Casey approaches him tentatively, swallowing his pride and dignity in favor of the ultimate goal.

Without even granting him the privilege of a glance, Donatello speaks, his voice like chant. "Raphael's in the living room, Jones."

Casey blinks. "How did you-?"

"Footsteps," Donatello answers before Casey can even finish the question. "And you don't smell like lavender enough to be April."

"I'm going to ignore the fact that you just smelled me, dude," Casey says with distaste making Donatello spin and send him a slight glare.

"Raph is in the living room." He repeats more dangerously this time.

And that's when Casey remembers why he is here in the first place. He grimaces and almost wishes he can control his temper and loud mouth like Raph does - compared to him that is. Of course, one look at Donatello's irritated face pastes a satisfied grin on Casey's face instead.

Donatello's frown deepens at the sight and Casey clears his throat. "Actually, I, uh, came to see you."

That snaps the turtle's attention at least. "Me?"

"Yeah, I kinda need your help," Casey says scratching his neck, "See, April's at Irma's having some girls' night-out crud and she sorta cancelled on me. Well, on our trig tutoring session."

The smallest of smiles plays on Donatello's lips at the news. "And that is my problem because-"

It takes a lot of effort in Casey not to pummel the snarky little mutant to the ground in that moment.

"Oh, come on! I'm fluncking here, dude. If I don't pass tomorrow's exam I'm done for in the hockey team. You gotta help a friend out!" Casey tries to say this in the most polite way of course, but somehow it ends up sounding like a threat.

The turtle is not at all intimidated as he crosses his arms. "We're not friends. We just put up with each other for the sake of Raphael and April."

"True," Casey agrees and lifts a finger smartly. "What if I paid you?"

"I'm not interested in your money." Donatello snorts.

"Good, 'cuz I haven't got any." Casey replies and Donatello raises a curious eyebrow. Casey shrugs. "I was thinking of giving you my share of pizza next time we order?"

The mutant openly laughs at that. "Who do you take me for? Mikey?"

"Fine! What do you want?" Casey groans helplessly and the dorky imbecile has the audacity to give Casey his freaking shell again.

"I want you to get out so I can keep working," Donatello says to the experiment before him.

Casey's hand travels to his back and grasps the handle of his hockey stick. He feels the need -the urge- to unsheathe it and test just how hard that brown carapace is.

He doesn't. Instead he tries to remember some river and stones crap Raphael once told him as he walks over to Donatello. He leans against a cabinet next to the worktable so the turtle can see Casey's smile.

The mutant doesn't like his expression in the least. It is distracting and Casey takes pride in that. Donatello stops tinkering with what appears to be a broken alarm clock to glare him down expectantly. "You're not going to leave any time soon, are you?"

"Nope." Casey answers picking up a mini screwdriver from the table and turning it around his fingers.

Donatello snatches the tool out of his hand. "You're like a horrid Michelangelo and Raphael hybrid walking nightmare."

Casey ignores this because he is not exactly sure what a hybrid is. So he just glances down and focuses on his vigilante uniform.

"You know," Casey says testing the sharpness of the nails popping out from his hockey glove, "April wouldn't have to tutor me all the time if someone else took up on the job."

This is when Donatello's expression shifts. It looks like he sees the point in Casey's statement.

Jackpot.

And the look vanishes.

Crud!

"Why me?" The mutant whines. "Surely you have friends who know trigonometry other than April."

Casey Jones' face falls, because he knows the turtle should be right. Should be. But he would never voice this to someone who doesn't even like him. So instead he does the smart thing and turns the conversation around before Donatello can figure it out. "'Cuz April won't shut up about how you're the smartest guy she knows."

"Really?" The stupidest of grins rises on the turtle's colored cheeks. "April said that about me?"

"Yeah, yeah, you're her geeky idol, whatever." Casey dismisses with a wave. "You gonna help me or not?"

Donatello hesitates before putting the tools down the table. "All right."

"Really! Awesome, dude, I owe you one!" Casey beams and pats the turtle's shell.

"Not so fast." Donatello takes his hand off his shoulder. "I do have a price, Jones."

"Oh, what is it?"

"You come with me to the junkyard and help me pick stuff up, for a month," he says.

Casey grimaces. He has heard the rumors about Donatello's junkyard trips. He has no intentions of breaking his back while dragging a freaking rocket engine of some sort down the sewers of New York, thank you very much.

Donatello's voice brings him back to the situation at hand. "That's the price, take it or leave it."

"Take it!" He replies because he loves hockey more than anything else, and right now this turtle is his only hope.

He even smiles a little when they shake on it.

It doesn't come as much of a surprise when Donatello reaches boiling point.

"So, just to get things straight." He massages his temples and breathes slowly. "You don't know what a hypotenuse is, you have never heard of Pythagoras' theorem and your test is at seven thirty AM, is that correct?"

Casey winces. "Yeah. You summed that up pretty well."

"And six hours ago, when I explained how to find the sin of theta and you clearly nodded and said you understood, you were just bluffing?"

Casey nods again. Donatello returns the gesture.

"And you're telling me this now." There isn't even a question this time.

"Dude, I told you I needed help!" Casey reasons.

"Well Casey, while 'admitting it' is the first step to recovery," Donatello says sweetly, "I don't have the resources to cure your complete and utter puckheadness!"

"Oh come on, it can't be that hard!" Casey says inspecting the book frantically.

"Of course it's not, this is basic trig!" Donatello explodes slapping his head then continues more to himself. "How on earth have you gotten this far at school?"

"Dunno." Casey shrugs, now feeling a little ashamed of himself. Why can't he get anything right? It's not like he hasn't been trying. It's not his fault numbers are not particularly good to him or any other subject for that matter. Maybe the teachers are right. Maybe he is a lost cause.

Donatello seems to pick up on his lousy mood change at five thirty in the morning and he pats Casey's arm. "C'mon."

Casey is not expecting this and at first thinks his new tutor has given up. Just like the ones before April had. "What? Where?"

"We're going to put this to practice." Donatello moves towards the door.

"Uh, in case you haven't noticed, dude. I haven't understood a thing you've said since two in the morning." Casey rises to his feet but follows him out the lab.

"I have noticed," Donatello tells him with tired eyes and makes a bee line for the lair's entrance.

They reach the Shellraiser and the turtle hops in. But instead of closing the door and driving off, he goes directly for a trap door on the floor and opens it. Instants later Donatello is gone and in his place the coolest turtle shaped motorcycle Casey has ever seen pops from the van-like vehicle.

It hatches open.

"Get in." Donatello turns the handle around and the bike purrs like a cat.

"What?" Casey steps back. "Listen dude, I admit you're not as bad as I thought you were, but I just don't swing that way."

The dry look on Donatello's face is murderous. "We're not driving off into the sunset, you knucklehead buffoon. I'm taking you outside because I need some fresh air and you need another approach. Get. The heck. In."

Casey hesitates but complies. He sits behind Donatello and, much to his shame, puts his arms around the shell feeling nothing less than a sissy. "Just so we're clear," he says over Donatello's shoulder, "we're never talking about this."

"Agreed." Donatello replies with the same embarrassed tone as he takes off.

It doesn't take them long to reach their destination. A deserted alley. It is unsurprising considering he's dealing with mutants here. Casey doesn't complain when the ride is over and leaps out of the vehicle the first chance he gets. It is just when they are on the rooftop next to the alley that the question blurts out. "Why didn't we take the Shellraiser?"

Donatello groans as if the answer is obvious. Casey hates this because Raphael's brother treats him like he is the sewer's imbecile. "Well for starters it's going to be dawn soon and the Shellraiser draws too much attention. Also, the stealth-bike is faster and can easily avoid traffic while passing up unnoticed and finally, that wagon requires at least three people to operate properly. And I'm not willing to risk the delicate engineering of my vehicle unless strictly necessary, meaning an emergency."

"Jeez fine." Casey snorts and then mumbles, "It was just a question."

He takes a couple of seconds to inspect his surroundings and doesn't even fake his look of puzzlement. It's too darn early for that. "So what the heck are we doing here?"

His answer is a blow to the chest. Casey has no time to duck or even protect himself. He ends up on the ground. "What the heck was that for?" He demands and instinctively takes out his hockey stick.

"I told you, you need another approach." Donatello tells him innocently, but the satisfied of lights is dancing in his eyes. Casey wants to wipe it out.

"And this is your kind of approach at trig? Kicking my ribs off?" Casey demands pointing his weapon at the turtle while his other hand grasps his sore chest.

"Of course, just now, we made an invisible triangle; see my leg's the hypotenuse, the longest side. While the opposite side is partly you, from your chest downwards until-" Whatever Donatello wants to say, Casey cuts off by placing a fist to his jaw.

"Explain that theorem!" Casey bites standing over the now fallen mutant.

Donatello gets up and shoves Casey, but instead of fighting him, the turtle spins around him and snatches the hockey stick out of Casey's hands. He throws it to the floor and before Casey can even register what on earth he is doing, Donatello takes another of his weapons from its shaft. This time it is Casey's bat that ends up on the tiles and forms a perpendicular line with the hockey stick. Finally the turtle takes out his own bo stick and connects the opposite corners of each end of the weapons forming a triangle.

Casey is at complete loss when the turtle kneels on the ground and takes out chalk from God knows where and starts doodling like his little sister would on her playground. When Donatello finishes he lets Casey peek on the piece of art. Turns out, Donatello had not only wanted to kick Casey but he also relished in the fact of making the moment last as long as he could. He has drawn himself kicking Casey again. And much to his dismay, Casey has to admit that this is a lot clearer and less painful than the real thing.

"This is an irregular triangle, you get that right?" Donatello asks and Casey nods.

The patronizing stare Donatello sends his way is enough to have Casey talking. "It's irregular because all the sides are different, okay?" He isn't an idiot, despite what this condescending jerk thinks.

"Good, not everything is lost," Donatello says and ignores Casey's growl. "Now if a triangle has three different sides in length it means each angle is different see? Let's call this angle theta..." He points at the sign that looks like a pokeball...

An hour later, Casey cannot absorb or scribble any more numbers down. At least this makes more sense now. After Donatello's lecture on how everything in this world uses trig, things get a lot clearer for Casey. Turns out, trig is easier to understand with real life examples and even some kicks and punches.

"Okay Donnie, I'm beat, let's call it a night and go home." He says not even bothering to call the turtle by his full name anymore. It is too darn long and complicated at this hour.

Donnie lets out a yawn. "Actually, it's almost six thirty. You have an exam and I have training."

He moans and Donnie echoes, agreeing.

All Casey wants to do is sleep. But of course not everything in this world turns out the way Casey Jones wants it. Because in the next couple of seconds they are not alone in the doodled rooftop anymore. Donnie groans and reaches for the fallen bo on the floor which at the current time happened to be a hill for Casey's doodle of a race car. "This day is never going to end is it?"

Casey mimics his friend and picks up his own weapon. They both stand back to back facing the Footbots that surround them. "Time to put everything I've learned to practice."

And with that they both dash forwards. Casey takes pride when the opposite side doesn't stand a chance against hypotenuse. The Foot falls into the ground.

Ms. Phelps slams her hand against Casey's school desk. He bolts up immediately and stands into a defensive. "Sin Ɵ is equal opposite over hypotenuse!"

The laughter that surrounds him reminds Casey that the trig exam ended over four hours ago. Ms. Phelps is not amused. "As much as I admire your enthusiasm for trigonometry Mr. Jones, this is Literature class. And I would appreciate if you refrained from snoring during Walt Whitman's lecture."

"But, isn't he dead?" Casey asks before processing his words and the teacher's features wrinkle like old paper.

"Sixteen thousand word essay, Mr. Jones, on Mr. Whitman's legacy. Due tomorrow," she says and walks off like a boss, leaving Casey's jaw hanging.

"Casey!" April's voice is too darn loud in his ears. She catches up to him before he can reach his locker. "Congratulations on your test! Looks like you're going to stay in the hockey team after all!"

"What can I say? I'm a genius." Casey shrugs as if his B minus is the best thing in the world. And it totally is.

April laughs a bit. "I hope my absence didn't give you much trouble last night."

Casey blinks and coughs debating the answer. In the end, he just huffs. "Nah! It's just basic trig."

"Cool so, I take it you won't need my tutoring anymore?" She asks with a knowing smile.

"Well -" he starts but April doesn't let him finish.

"Great! Because Irma and I are catching a late movie tonight!" And just like that she runs off, leaving Casey to mop around in his current dilemma.

"But I have an essay due to tomorrow!" Casey whines at the empty hall then a sudden idea clicks in place. He takes out his phone and dials.

"Not you again."

But Casey only beams. "Donnie, my man! What do you know about Walt Whitman?"

I need a bromance episode that focuses on Casey and Donnie working together for the greater good. Which in this case is passing trig.