A HEAD EDGED THROUGH THE WATER, ALMOST as wide as the tunnel. The creature’s skin was as smooth as a beach pebble, gleaming in the faint light.

Max and Lia backed away.

Two tiny unblinking eyes like dull black marbles watched them.

The Beast’s body followed, huge lengths of snaking pale flesh spilling into the cavern.

It’s a gigantic eel! Max realized.

As the creature’s tail finally slid from the tunnel, the body formed into a tight coil, filling almost half the cavern. Its staring head came to rest over its back and its lipless mouth parted to reveal jagged, close-packed teeth. Max made out a robotic harness behind its neck, just like the one worn by Cephalox the Cyber Squid. Metal clasps and coils of cable sat next to the eel’s pale flesh — the mechanism by which the Professor controlled his slave. Mounted on top of the harness, under a glass dome, was the second piece of the Skull of Thallos. Max peered closer — it was an eye socket and a section of cheekbone.

Lia lifted her pearl spear and Max raised his harpoon gun.

“Why isn’t it attacking?” he hissed.

With a click and a whir, a panel on the harness slid open. A red orb, like the one Max had seen on Cephalox’s tentacle, swiveled around and jerked closer. It blinked like an eye.

“Hello, Max,” said a voice, deep and distorted by electronics. “Welcome to the lair of Silda.”

“Who are you?” shouted Max, loud enough to disguise his fear.

“You can call me … the Professor.”

Max felt his stomach jolt at the sound of his enemy’s voice. He could see there was no place for the Professor to hide on the eel’s body. He must be controlling it remotely, thought Max.

“How does the Professor know your name?” whispered Lia.

“I don’t —”

“Your father told me you were clever,” continued the voice, “but now I’m beginning to doubt that. You walked right into my trap.”

Trap?

Max glanced at Lia, then at the metal walls. There was only one way out, and they’d have to get past Silda to reach it.

“Where is my father?” asked Max.

“Safe,” said the Professor. “For now. Which is more than I can say for you two. There’s no escape from here. Silda’s lair will be your grave.”

Max raised the harpoon gun. “We’ll see about that.”

“Ah, my old weapon,” said the voice. “That brings back memories.”

Of course! thought Max. “The crashed sub belonged to you!” No wonder there were no bodies in the sub.

Rivet surged forward on speeding propellers and clamped his jaws over Silda’s tail. A crackle of blue lightning shot along the Robobeast’s coils and over the dogbot. Rivet’s metal body spasmed, his legs quivering, then he drifted away.

Max wanted to go to the dogbot, but he couldn’t leave Lia. “Silda’s an electric eel!” he said. “Don’t get close.”

Rivet was making strange noises — buzzes and pings. Just like back in Aquora when I’d only just built him and I put his circuit board in the wrong way, thought Max.

Now he understood the metal walls. If Silda touched them, they would become electrified. There was no way out, and fighting the Professor’s creature was going to be even more difficult than Max had thought.

Silda uncoiled slowly and nosed through the water after the stunned dogbot. The Robobeast opened its mouth.

“No!” shouted Max, swimming between the gaping jaws and his dogbot. He aimed the gun and fired, launching the harpoon. Silda slunk to one side as the missile cut through the water, a wire snaking out behind it. The barbed point punctured the eel’s side, and a blue pulse shot back up the wire and into Max’s arm. It felt like something had grabbed his spine and snatched him through the water. His hand clamped on to the gun as the current zapped through him.

Max couldn’t feel a thing. He saw his limbs sprawled in the water, but when he tried to move them, he couldn’t. Slowly, his skin began to tingle all over with pins and needles. The harpoon gun drifted through the water, out of reach. Great. Now I haven’t even got a weapon, he thought.

“Are you all right?” asked Lia, arriving at his side.

Max managed to nod. Lia tugged him away from the eel’s mouth.

“I thought you were dead!” she said.

“So did I,” said Max.

Thankfully, Rivet seemed to have recovered. He was barking angrily in front of the eel’s head, retreating just out of reach.

Max struggled upright in the water. “We have to get that harness off,” he said. “That’s how the Professor is controlling the Robobeast.”

But as he pointed at the harness, he saw more blue splinters of light crackling across it. There’s no way I’m touching that, he thought.

“How are we supposed to deactivate the harness if we can’t even touch it?” asked Lia.

The red camera eye rotated to face them.

“Uh-oh,” said Max.

Out of the corner of his eye, he saw the eel’s slab of a tail arcing through the water. Barely stopping to think, he pushed Lia backward. She gave a squeak of surprise as she tumbled clear, and the tail smacked into him. Electricity surged through his limbs. It felt like his skeleton was being ripped out of him as he spun through the water toward the outer wall. Then he slammed into the metal and another shock vibrated across his skin.

Max drifted in the water, every nerve on fire, unable to move.

I was lucky with the first Robobeast, he thought, but this one’s going to be the end of me….

Silda’s huge head rose through the water to face him. The eel’s mouth parted in what looked like a horrible smile.

“Met your match this time, haven’t you?” said the Professor. “I bet you wish you’d stayed in Aquora now.”