DOZENS OF LARGE plastic cubes, each bigger than her nest back home, lined the widening dirt path. Aluna stumbled to the first cage and saw a Deepfell floating inside. She recognized the slave collar around his neck and the dead look in his eyes.

The second held a young man that looked like a Kampii, except he had a long, sinuous snake body where his fish tail should have been. His tail coiled around and around. Gold hoops hung from his ears, and half of his long, dark hair had been shaved to stubble. His eyes were bloodshot, but there was still intelligence in them, still some spark of life.

She walked over and put her hands against his cell.

Suddenly, he pounded his fist against the plastic and shouted. She jumped back. His words were muffled by the cage.

“I don’t understand,” she called back.

“Shhh!” Barko said. “No yelling. No yelling!” He danced around nervously and looked up the path. “Faster now, mermaid. No time for the Mess-ups!” He bolted forward, and she had to follow.

She wanted to stop and talk to all the creatures trapped in the cages. They passed a dolphin and a baby shark, a huge white bird and a striped cat so big that Aluna’s whole body could have fit inside her mouth.

Another cage held a creature that was Human from her head to her waist and horse below that. An Equian! Her back left leg had been replaced with a metal blade that sparked as she stomped. Deep red gashes and scars ringed the metal where it connected to the horse-woman’s flesh.

The dog pulled Aluna along. Her stomach knotted tighter and tighter as they wove quickly through the captives. So many had been altered. She saw metal tusks added to a deer and a huge tortoise with jagged razors attached to the rim of his shell and some sort of saddle mounted on his back.

So much suffering, so much loneliness, so much pain and loss. Sadness rolled from the cages in waves, suffocating her heart. What kind of person could do this? What kind of monster? She couldn’t save only Daphine, not anymore. Now she had to save them all.

Barko bounded down the path, ignoring all the cries and dead eyes of the captured creatures. Aluna felt tears well in her eyes and trail down her cheeks, but she didn’t stop. She couldn’t. There was only forward.

The path emptied them into a bright clearing surrounded by cages, some occupied, some empty. She didn’t have time to study their occupants. They had arrived at the very center of Middle Green, at the very center of HydroTek. And the man — the thing — crouched by the last cage with his back toward them could only be Fathom, so-called Master of the Sea.

He likes parts, the dog had said, and Aluna finally understood what he’d meant. Maybe Fathom had looked Human once, but now he was a patchwork monster. Two dorsal fins jutted from his shoulders, fins that must have belonged to Deepfell before they were ripped off and reattached. His left arm had been split into two. One limb ended in a mechanical hand, and the other had some sort of artifact control pad screwed onto the end. The bottoms of Fathom’s legs had been extended to twice their normal height, with dull-black metal bars wrapped in wires and tubes.

She couldn’t even identify the other bits of flesh and metal stitched and embedded all over his body. Some oozed blood as she watched. Worst of all, the back of his skull had been replaced by some glasslike material. She could see right into his brain.

When he turned and rose, Aluna gasped. Not only was Fathom’s face still fully Human, but she recognized his tousled brown hair and glasses from the photo Hoku had pulled from Sarah Jennings’s water safe.

Fathom was Karl Strand.

But how? That letter was written hundreds of years ago! Karl and Sarah were together before the Kampii even existed. How could he still be alive?

Fathom smiled, looking even more like the man from the photo. But when he spoke, it wasn’t to her.

“Well, dog,” he said. “What have you brought me today?”

The dog sketched a nervous doggy bow and said, “A mermaid, master! A mermaid for your collection!”

Aluna looked at Barko, surprised at his betrayal, but the dog ignored her gaze.

“Pity, dog, but there will be no reward for you today,” he said. “You see, I already have a mermaid.”

Fathom motioned to the water-filled tank he had been inspecting when they arrived. Aluna had assumed it was empty, but it wasn’t. The occupant had been cowering in the far corner, curled into a ball. When Fathom activated the control device in his double arm, the creature yelped and swam obediently to the front of her enclosure.

Fathom’s mermaid was Daphine.