"The grotto would have been better," says Batman, without looking up.

Kaldur blinks. He's not sure what he was expecting Batman to say, but it wasn't that. 

"...sir?"

Now Batman looks up. He looks at Kaldur, and enters Instructor Mode.

"Your opponent was trying to locate you through auditory perception, and unfortunately for you, water conducts sound. In a more open aquatic environment, like the ocean floor, this could have been used to your advantage to confuse where your location might be. But you didn't have one of those available. You had two major sources of water to hide in. This one is open, and as you noticed, consequentially open to ambush from above. The grotto is not. Furthermore, it's smaller, and has better acoustics."

Batman pauses, to see if Kaldur sees the implication. 'Better acoustics' seems like a terrible set of words when dealing with an opponent that tracks by auditory perception, but realistically, there isn't a way for Kaldur to have hidden from Rain's superhearing without better equipment and training. Instead, it would have been possible to go in the complete opposite direction, and create so much sound in an enclosed space that Rain couldn't detect where in the room Kaldur was. It probably wouldn't work either, Kaldur is sort of at a major disadvantage here, but it would have given him more room to work with.

"Thank you for the advice," Kaldur replies, looking thoughtful. Acoustics...Rain's enhanced hearing could leave him more vulnerable to deafness, or noisy distractions. This game is already proving its worth for their development as a team: it's useful to know a teammate's weaknesses so that one can compensate for them. 

He holds out the rebreather. "I believe this is yours?" 

"It's what I'm here for. Yes, it is, thank you." He then goes right back to what he was doing.

With utmost seriousness and gravitas, he adds: "Keep up the good work, both of you."

Rain smiles, then clears his throat and decides that it is time to just casually carry on as if he did not get punched somewhere sensitive.

"Can you use magic to find my sister?" he asks Kaldur, brightly.

"That...depends on how thoroughly she is hiding," Kaldur replies. "I am far from a master of sorcery."

This is probably not the best time to admit that he dropped out of his sorcery training to become Aqualad. 

"Better than I am! And she might not have thought to hide from you. After all, I'm the one seeking."

"True. Since you are not a sorcerer, she may not have thought to hide her magical presence."

Kaldur closes his eyes and focuses. The tattoos on his arms glow blue through the sleeves of his tracksuit as he reaches out with his sorcery, searching for Yvette. 

There are the subtle patterns of carefully woven magic over the whole base, distinguishable only because he's on the correct side of the magic hiding them from outside view...

... And almost directly above them, a bright and burning aura of active magic.

He's surprised enough that he loses concentration and drops the threads of magic. Laughing, he tilts his head back to look up at the ceiling.

"Can you jump that high?" he asks Rain. "Or should I give you a ride?" 

"Ride!" asserts Rain, grinning. "I can probably jump that high, but you know where she is and I don't."

—Shit, shit, shit, shit, shit, why didn't she think of that? Of course she doesn't know how to disguise herself from other magic users yet! There are approximately no magic users to disguise herself from up here! Why didn't she take that into account, she even hid in the same room as Kaldur! That's just upsetting, if she gets eliminated second despite her best efforts she is going to be so annoyed.

Luckily, just standing on the ceiling inaudibly invisible is not the entirety of her bag of tricks. She already has her chalk out and is drawing.

The tattoos light up again as Kaldur pulls out his Water-Bearers and starts drawing water from the convenient pool right next to them. 

As the water builds up beneath his and Rain's feet, they are lifted towards Yvette on a platform that's a lot sturdier than it looks, and rising by the second. 

The ceiling is tall enough that she has some time. She draws a door to match the one she set up before she hid here, then decides that having easy access to a very tall ceiling is worth the time investment, and draws a second rectangle in magic chalk.

Then she activates the first door and climbs through it to arrive in a completely different part of the base. Hey, fair's fair, right? The two of them may have a front row seat to a chalk rectangle changing into a doorway to another part of the base.

She closes it behind her. A second, inert rectangle sits beside the first.

He sees it, speeds up—but not enough to catch her before the door closes.

"She's gone," he reports to Rain, who probably guessed already. "That was a portal of some kind." 

Since they no longer need to be near the ceiling—he doesn't think he can re-open the portal—he starts letting the water recede back into a more natural configuration. 

"Yeah," Rain agrees, thoughtfully. "Hold on, don't put us down yet—she didn't just go through the portal. She drew another rectangle first." He points. There are two rectangles on the ceiling; one in grey, one blue. The grey one had been the portal. "I bet she had a good reason, otherwise why waste her time and risk getting caught?"

Squint.

"I believe it is the first half of an inactive portal—useless until the second half is drawn. We cannot use it to follow her...but if we destroy it, she will no longer be able to use it either." 

...he flicks a stream of water up at the blue rectangle, aiming to make a gap in one of the edges so it's no longer a complete shape. Hopefully the chalk isn't water-resistant. (The grey rectangle, now it's been used, doesn't look like it would work again; he leaves it alone rather than wasting water and effort.) 

It is not water-resistant! It washes away easily.

"Yeah. Good idea. This is a bad spot for the other half of a portal. Too hard for one of us to stay up here to ambush her when she comes through. Maybe we can with others, though. I bet she's going to do this again."

...Kaldur blinks, then grins.

"That is not a strategy I had considered," he admits. "It could prove fruitful." 

Now, where might Yvette have ended up...

The answer is: invisibly looking for another spot to draw out portals. Clearly she can't hole up on the ceiling somewhere again, Kaldur can sense her magic (which feels very unfair, but isn't), so it's instead time to play keep away. If she has her way, she's going to have portals absolutely everywhere. But getting them spread out is hard, she's drawing all of these out herself and that involves a lot of running around. She predicts she's going to be very tired by the end of this; running is not her forte.

She vaguely regrets not putting more effort into PE or picking up some kind of sporty thing that would have made this easier, and jogs down a hallway, looking for places to hide portals as she goes.

There's a red blur streaking down the corridor—

—and then Nate runs straight into her, knocking them both to the floor. 

"Ow! What the hell?" 

She yelps as she goes down.

"Ow," she mumbles. Still invisible. "Hi, Nate."