NOTHING RUMI’S SEEN before could compare to this. The heat and the chill, the darkness and the light, all combining into a roiling mass . . . it’s something that should exist in some other time, in some other world, but it is right in front of him. Rumi’s undone, his mind whirring as he watches.

Auriel isn’t undone, though. He looks down placidly, then looks back at Rumi. He really sees Rumi, and the tree frog realizes it’s for the first time. Until this moment, Auriel has treated the shadowwalkers like inanimate objects, like moving trees or grasses. But now the enormous yellow snake seems to be trying to communicate something.

“What do you need me to do?” Rumi asks. Even at a whisper, his words boom in the water.

Auriel shakes his head. Nothing. Then he looks down toward the roiling mass of magma and dark water. He looks back at Rumi.

“What are you thinking?” Rumi asks. His skin is already crawling from the heat and salt, but also, now, from an extra source of tension: What is Auriel planning?

Auriel flicks his tongue up in the direction they came. Go back.

He wants Rumi to leave?

Rumi shakes his head. Retreat before they’ve accomplished their goal? No way. His lungs feel empty, like his front ribs are pulling against his backbone, but he’s got some time left down here yet before he starts really suffocating.

Auriel turns his attention to the steamy cauldron down below. He flicks his tongue out, tasting the hot salty water, laced with ash and bits of rock, so far below the surface of Caldera.

Then Auriel moves.

His thick, glowing body ripples through the water as it descends toward the surging magma and water.

“Auriel!” Rumi calls. But there’s no chance Auriel could hear him over the boiling turmoil below. Rumi can only watch as the bright yellow beams cast shadows over the undersea cavern, lighting mysterious glints of this innermost cavity beneath their rainforest home. Auriel’s powerful coils propel him down, down, until he’s nearly at the source of the magma itself, at the red-and-black boil that is the center of the plumes of ashy water.

Auriel swims right in.

The moment his head touches the magma, there’s an explosion of light, light that is also liquid as it blooms from the boa constrictor’s body. Then the body itself bursts and explodes, all the light that it contained blasting out into the water.

Auriel is gone.

Rumi’s dazzled by the sudden illumination, is still reeling from the brightness of it when the first shock wave reaches him. As it does, his eardrums fill with a booming noise, and the force of the water surge knocks him against the cavern wall. His bones creak, and he tastes blood in his mouth. As he kicks out in the darkness, the stones around him rumble and shatter, deafening him and buffeting his body with powerful currents. It’s impossible to know which way to go, how to avoid being pushed farther below to drown, how to avoid the invisible shivering boulders plummeting all around.

As Rumi flails in the water, he glimpses an orange-yellow light. His impulse is to head toward it, toward sunshine. As he makes his first stroke in its direction, though, he realizes that it’s not daylight he’s seeing; it’s the last of Auriel’s explosion. It’s exactly where he should not be going. He reverses course.

New waves of hot ashy water push against Rumi, searing his skin even as they fill his senses with rocks and soil. At least these painful currents are pushing him away from the blast. He rockets along the passageway that he used to reach the underground cavern, right up the chasm and through the next passageway, pinging off the walls and ceiling, trying to stay alert and conscious despite the many blows to his head.

Rumi’s world is only dark roaring, and he loses all orientation. He rockets down a side passage that narrows suddenly, until—thup!—Rumi is wedged tight. He struggles to free himself, but there isn’t enough strength in his tiny arms and legs. More hot water from the explosion pushes against his legs, scalding them. The pressure is greater and greater, the agony making Rumi cry out into the dark water of the ocean depths. It’s not just his flaying skin; his muscles and bones are squeezed by the pressure . . . until suddenly Rumi shoots free, zooming forward. There’s no directing where he goes, not at this speed. He scrunches his eyes shut, puts his arms over his head, and hopes he doesn’t wind up splattered against a rock wall or impaled on a sharp outcropping.

Instead, he can feel the current slowing, the water around him chilling. Rumi opens his eyes again, and reaches out his arms and legs, trying to feel what’s nearby, where he might be in the system of caves.

It’s impossible. He’s not in a cave. He’s swimming in wide-open pitch-black water.

Rumi shivers uncontrollably. Is this the end? There’s no point swimming in any one direction, not when he might be bringing himself even farther from safety.

“Hello?” he croaks in the water, using his air magic to amplify the sound. “Hello?”

Only darkness and silence in reply.

“Hello?” he tries again.

A shift in the black. It ripples.

Rumi squints.

In the center of the ripple, an arrow of flame holds steady in the dark.

Gogi! The air bubble must be back.

“I’m coming, I’m coming!” Rumi chirps as he strokes his cramping legs through the water.

The orange arrow nears and nears until . . . plop. Rumi passes through the membrane of the air bubble, bouncing twice on the ground before he comes to rest on his back, gasping for air.

Three beautiful faces above him: a monkey, a sloth, a macaw. “Oh my gosh,” Rumi manages to say. He wants to make words, but can’t get his brain to form them. I am so glad to see you three. I was worried I wouldn’t, that I wouldn’t be able to say good-bye.

“We’re glad to see you too!” Gogi says, as if reading his thoughts. “When we heard you slipping down, and then Auriel disappeared, we had no idea if you were okay, or if you were even still alive.” Tears run down his furry cheeks, already wet with seawater.

Rumi manages to get his muscles to coordinate well enough to sit himself up. “Auriel!” he gasps.

“What about Auriel?” Sky asks.

“Sacrifice . . . boom,” Rumi sputters, for once at a loss for any big words.

“Um . . . guys?” Banu says.

“Auriel is dead?” Sky asks, feathers drooping.

“Yes,” Rumi says.

Sky blinks his eyes heavily, the feathers on top of his head going flat.

“Sacrificed himself . . . saved us . . . made explosion . . . against magma,” Rumi manages.

“Guys,” Banu presses.

“Oh my gosh,” Gogi says to Rumi, rocking on his heels. “Auriel has been trying to get to this moment, fought to rush us underwater, all because he meant to sacrifice himself. I think this was his plan all along.”

“Guys!” Banu says, raising his voice for the first time Rumi has ever heard. “Would you take a look at that?”

Rumi follows Banu’s gaze. Through the expanse of black water, he spies a chaotic jumble of stone and boiling water, all backlit by the orange lava beyond. “That’s where Auriel plugged the magma flow,” Rumi says.

“Yes . . . but look what’s . . . happening to it.”

Now Rumi sees what’s gotten Banu’s attention. The magma is mounting up behind the blockade.

Auriel’s fix won’t last for long.

“One implosion isn’t enough to stop the force of all that magma,” Sky says. “We shouldn’t have gotten our hopes up. The pressure has to be even higher than ever.”

“Maybe we should make a run for it,” Gogi says, his voice squeaking off at the end.

“More pressure than ever,” Rumi says, tapping his lips. “More pressure than ever.”

“Yes. So let’s make a run for it,” Banu says.

“Hold on,” Sky says. “What are you thinking, Rumi? Hurry! We only have a few seconds.”

“More pressure than ever . . .” Rumi repeats.

His mind goes to the fish egg he saw in the pictures back in the Cave of Riddles. How it bulged out everywhere, until the two-legs lanced it.

Back then, it had seemed like a portrait of cruelty. But maybe, maybe—

“It was a message!” Rumi shrieks.

“Okay, super, you can tell us all about it later,” Gogi says.

“Auriel plugged the one hole that was right under Caldera. But that’s only the first step,” Rumi says quickly.

Sky swings his head back and lets out a loud caw. “We have to release the magma a safe distance away from the rainforest, before it comes back out here!” he exclaims.

“The place marked with the X on the tunnel map,” Rumi says.

“Can you lead us there?” Sky asks.

Rumi nods. “It was one and a half frog-lengths into the tunnel on the map, which could calibrate to maybe a thousand frog-lengths back along the real live tunnel.”

“Enough talking, more doing!” Gogi says frantically, his eyes on the intensifying magma glow.

“Hold on!” Rumi cries. He chirps for joy. Finally he doesn’t have to think about what’s the right course. He just knows it, feels it deep in his bones.

Rumi opens his mouth.

He lets out the biggest stream of wind he’s ever made.