Six gems on Sapphire Saraphina's tail had gone dark. She counted them again as she sank into the trench, because counting was the only thing that slowed her fear. The dark spots climbed from the tip of her tail toward her body. She had watched two other merpeople lose their tails to the same cold. Now she chased that cold to its source, hoping to end it before the crown she meant to claim named a queen who could no longer swim. The trench floor lay below her in full black. She could feel the cold pull, a steady tug against her scales, but she could not see what made it. She pressed her palm to the rock and read the pressure the way she had all week. The pull came from a spot ahead. She swam toward it and felt another gem flicker and die against her hip. "Stop swimming blind." The voice was blunt and old. Thalassor Deepcurrent rose from the dark, an elder merman with silver hair and a golden pearl set in his tail. She knew him by that pearl. It marked his right to speak for the deep. He held a rolled tidal chart against his chest. "You're following the cold wrong. It's not one source. It's two." "Then help me find it," Sapphire said. "I lose a gem every minute down here." He unrolled the chart. It showed the trench and two thin lines of cold crossing beneath the floor. "Where they cross, that's your source. A thief pulled a relic from that spot. The current died after." His mouth went flat. "That's all you need." Green light bloomed to their left. A mermaid pushed through the dark, half her body frozen, half burning, cracks in her skin packed with glowing garnets. Crysa Embertide. Her flaming tail lit the trench floor at last. "I felt the cold too," she said. "It pulls on the fire in me." She said no more. Sapphire saw it now. The garnet light fell on an ice chest wedged in the trench floor, lined with emerald jewels, frost webbing every crack in its lid. The cold poured from inside it. She swam down and gripped the lid. Cold bit through her hands. Two more gems went dark as she pulled. The lid broke open. The pull stopped at once. The tug against her scales vanished, and the trench went still. Inside sat a shard of black stone. It drank Crysa's firelight and threw none back. As Sapphire stared, the dark spots on her tail held. They did not spread. But they did not heal. Her lost gems stayed dark. Thalassor looked into the chest and his face changed. "That's not a relic," he said. "That's what the thief was carrying it toward." He rolled his chart shut. "You didn't stop the cold, girl. You woke what was feeding it."