Seraphina Blue had counted the guard rotations at Moon Lagoon since she was eight, and tonight she meant to use them. She crouched behind the reeds with a coil of rope and a weight in her pocket. The plan was simple and stupid: sink herself past the shallow shelf, hold her breath, and pray the deep current carried her toward the prince's court. She had seen him surface once, years ago, during the red tide that made her cousin hide indoors for two days. He had not flinched at the waves. She had not stopped thinking about him since. She waded out past her knees. The water was cold and tasted of salt and old stone. She tied the weight to her ankle and looked down, and the lagoon looked back, black and far deeper than her lungs could manage. She thought of her neighbor crying through the storm. She thought of the prince's steady face. She lifted the weight to drop it. "You'll drown before the second bend." The voice came from a ring of stones she had passed a hundred times and never questioned. Shallow blue water glowed inside the circle, lit by shells wedged between the rocks. A merfolk had surfaced there, arms folded on the rim. He watched her the way a fisherman watches a hooked thing decide whether to fight. "That's where surface girls go when they try this," he said. "The second bend. The current folds them under." He told her the ring was a speaking place, set at the lagoon's edge so his people could meet land-dwellers without breaking the deeper laws. He had been watching her walk the shore for weeks. She untied the weight. She asked him why he was telling her. He shrugged and lifted a mask from the water. It was sleek and pale, shaped to cover her nose and mouth, with small orange lights along the jaw. "This breathes for you," he said. "Down to the court, if you can stand the pressure. I'm not giving it to you for free. You'll owe a favor, and I'll name it when I name it." Seraphina took the mask. She did not ask what the favor would be. She had already decided, standing in the reeds with a rope on her ankle, that she had no price she would refuse. He pointed across the water to a dark shape rising from the far shallows: a vine arch threaded with shells, unlit. "When that arch lights blue, you've been granted passage," he said. "Until then, you go down as a trespasser. The guards will be within their rights." He sank without waiting for her answer. Seraphina fitted the mask to her face. The seal pulled tight against her skin. She walked back into the water, alone now, with a borrowed breath and a debt she could not yet count.

Seraphina came back to the lagoon every night for a week. The mask sat in her bag, sealed and waiting. The vine arch across the water stayed dark. She crouched in the reeds and watched the shell at its crown catch the moon and give nothing back. Each dawn she walked home with the mask still dry. She learned the wards while she waited. On the third night she spotted them: thin metal rods driven into the mud along the shelf, each one strung with small mirrored discs. The discs turned when the current shifted. When she tossed a stick past the nearest rod, the water above it boiled white and the stick came apart in three pieces. She counted twelve rods between her crouch and the arch. She marked each one in her head and did not go closer. On the sixth night she brought a torch. It was an old thing she had pulled from her grandfather's shed, wound with swamp vine and capped with a blue crystal that would not go out in rain. She told herself it was for the walk back. She knew she wanted something in her hand when the light came. She set it in the sand beside her knee and waited. The arch lit on the seventh night. It did not flicker first. One moment the vines were black against the water; the next, blue fire ran through every twist of them, and the shells along the curve flared like small lamps. The crown shell threw a clean white beam across the lagoon and struck the sand at her feet. The gate had opened. Her hands shook so hard she dropped the torch and had to pick it up twice. She fitted the mask. The seal pulled tight against her cheeks and the orange lights along the jaw warmed. She walked into the water with the torch in her left hand and her right hand out for balance. At the first ward rod she stopped and watched the discs. They hung still. The blue light from the arch ran along the surface like a road, and the rods on either side of it stayed quiet as she passed. She counted them under her breath. Twelve. She crossed the last one and the shelf dropped away beneath her feet. She went under. The mask breathed for her. The torch burned blue in her fist and lit a column of water around her body, and below that column the lagoon kept going down, farther than she had guessed from the shore. She could see the shape of something built into the rock far below — pale panels, blue-streaked, folded like the petals of a closed flower. A gate. She kicked toward it. The shore was behind her now, and the favor she owed was somewhere ahead, and she did not yet know the name of either.