RIVET NUZZLED AT MAX’S ARM.

“You have to be strong, Max,” said Lia. “If we follow the Professor, we’ll find your father.” She reached into her knapsack. “Here, this’ll make you feel better.”

She pulled out a piece of seaweed cake and offered it to him.

Max smiled. “It wouldn’t be my first choice, but thanks.”

They swam across to a boulder at the side of the cavern and sat side by side. Max bit off a chunk of the cake and chewed thoughtfully. The Professor was an evil man, but he wasn’t stupid. He didn’t simply kill for the sake of it, and as long as Max’s father was useful to him, he’d be safe.

I just have to find him before his usefulness runs out….

“All we can do for now is follow the skull,” he said. “The Professor will be guarding the last two pieces with all his might.”

He swallowed the last of the seaweed cake, and called Rivet to him. Opening the storage compartment in the dogbot’s back, he took out both pieces of the skull. “What now?” he asked.

Lia took them from him and held the two sections together, matching their cracked edges. A flash of blue light made Max cover his eyes, but it faded quickly. When he looked again, the fragments of skull had become one, fused together without even a mark to show they were ever broken. The long jawbone jutted out beneath the powerful, staring brow. There was still a gaping hole in the middle of the face, and the top edges were broken.

“Thallos must have been a strange-looking creature,” said Max.

Lia scowled at him, but her smile quickly returned. The faint blue glow seemed to shine from her skin for a moment. “I can feel it,” she said. “The power is coming back.”

Max could sense something, too, as if the water all around was filled with life. Even Spike was staring, hypnotized by the skull.

“Tell me more about Thallos,” said Max.

Lia ran her hands over the smooth bone. “We have all sorts of legends, but nobody really knows much. He was an ancient creature, and a powerful one. Once the Merryn were wanderers — we traveled the seas in tribes. But the skull drew us together. By living close to it, we developed our powers.”

Max thought back over all he’d learned since coming underwater. Before the Professor had struck, the Merryn had the ability to control the seas. Not using barriers and tide-breaks and fancy technology like the humans of Aquora City, but with the power of their minds. They could communicate with every living creature under the waves, and lived in peace.

The Professor had ruined that when he took the skull and broke it. Even though Max had gills now, he still felt a little ashamed to be a human — a Breather. He knew he’d do everything in his power to help recover the other skull pieces.

Lia released the skull and it turned in the water, directing them away from the coral reef.

“Let’s go get the aquabike,” Max said. “I can’t keep getting lifts from Rivet.”

They swam back out of the cavern through the narrow passage and found the bike floating in the water. A small octopus had wrapped its legs around the handlebars and lazily detached itself as they approached. Max checked the controls and fuel gauge. “Should be fine,” he said, climbing into the saddle.

“We should rest first,” said Lia. “There’s a big ocean out there, with lots of dangers.”

Max opened his mouth to argue, but a wave of weariness washed over him. He hadn’t slept since he’d been in his bed on the 523rd floor of Tower Alpha Four; the place he’d once called home.

“You’re right,” he said. “But we can’t sleep in the open. The Professor might send one of his creatures after us.”

“I know just the thing,” said Lia. “Follow me.”

Max set the bike to CRUISE, and they traveled steeply downward, leveling off at the seabed. A carpet of bushy weeds rippled in the gentle current. Lia was scanning the way ahead and steered off to the left. The ground dipped away in a small crater, and at the bottom two giant spiral shells lay on their sides. Each was as big as an Aquora City transporter. The white edges of the shells curled away, perfectly smooth and speckled with pink flecks.

“Does anything live in there?” asked Max.

Lia shook her head. “Not anymore.”

She leaped off Spike and folded herself into the shell’s opening.

“Keep a lookout, Rivet,” Max said.

He parked the aquabike beside the shell and climbed in. The surface felt strangely warm and soft and made a perfect bed.

It wasn’t long before he could hear the soft rumble of Lia’s snores. Spike lay beside her with his eyes half-closed. Max knew that he’d fall asleep soon, but his head was still buzzing with thoughts. Once, a year or so ago, he’d stood with his father, watching the fishing boats draw up at Aquora docks. One of the fishermen, an old man with a white beard and deep lines crossing his face, had shown them a shell he’d dredged up in his nets. It looked like the ones they slept in now, but smaller, about the size of a clenched fist.

“There you go, youngster,” the fisherman had said, tossing the shell over. “A present for you. Close your eyes and hold it up to your ear.”

Max’s father had frowned, but nodded.

Max did as he was told, and pressed the cold shell against his ear. At once he’d heard an echoing, swirling sound, like crashing waves whipped by winds.

“Can you hear it?” the fisherman had asked. “The sound of the sea?”

Max smiled at the memory. He’d thought it was magic, those howling winds and the rush of water, trapped inside a tiny shell. His father had hated the sea ever since Max’s mom disappeared, but he’d let Max listen to that sound.

Max turned over in his shell bed to make himself more comfortable, and listened to the sounds of the sea all around him. Rivet lay in the sand on the seabed, his ears pricked up for sounds, his watchful eyes dimly red. Beyond him, a cloud of silver fish danced in the current like a thousand spinning coins. A school of jellyfish bobbed through the depths, trailing their fluorescent purple bodies.

His father had been right to be fearful — but Max wouldn’t let himself be afraid.

“I’m coming for you, Dad,” he whispered.

He only wished his father could hear him.