The Frost Twins stood knee-deep in snow and argued about which foot to move first. She wanted to cut west toward the low pass. I wanted the ridge. Our body did not move. It never moved when we disagreed. Wind pushed snow across our boots, and still we stood there, one head glaring at the other on the shoulders we shared. "West," she said. "The pass is faster." "The pass is watched," I said. "The ridge is empty." We are one ice fairy with two heads, a boy and a girl on a single body. Long ago something of ours was split in two. Neither of us can say what it was. Every time one of us tries, the other goes quiet, and the words drop away like snow off a branch. We are traveling to the frozen lake where winter was first born. We believe the other half waits there. We believe finding it will make us whole. A small shape burst from the pines above us, a spotted fawn with pale wings, chased by nothing we could see. It skidded down the slope and stopped short of our boots, sides heaving. She reached to steady it. I reached to check its leg. Our arms crossed and locked. The fawn bolted before either of us could touch it, straight down the slope toward a cluster of blue lights we had not noticed before. We followed, because for once we both wanted the same thing. The lights grew into windows. The windows grew into a home built from frost and pale stone, tiered like shells stacked on shells, with stairs of clear ice curving up its face. An older fairy watched from the lowest step. Her wings were folded flat. She did not smile. "You are the two-headed one," she said. "You want the spell no fairy has finished." She looked at each of our faces in turn. "I taught the last student who tried. She froze her own heart trying to cast with a will she did not have. You have two wills. That is worse, not better. I will not teach you." She turned to climb the stairs. I opened my mouth to beg. She spoke first, without looking back. "Come inside. Sleep one night. In the morning I will tell you where to find someone who might. I will not, and I will not watch you die on my step." She left the door open behind her. Inside, past a narrow hall, we saw a single bed made up for two, and above it a portrait of a boy and a girl rendered in cool blue, the frame cut from ice. We stared at the picture. Neither of us spoke. Our body would not move.

The door stood open behind us. The portrait held us where we stood. A boy and a girl in cool blue, framed in ice, hung above a bed made for two. Our body would not move. She stared at the girl. I stared at the boy. Neither of us knew who they were, but we both knew what they had been: a student the older fairy had taught, and someone she had loved enough to hang on her wall. "She said one student died," I said. "There are two faces." "Then one of them watched," she said. We crossed the room together for the first time all day. On a low shelf below the portrait lay a pair of throwing knives, twin blades cut with matching snowflakes, the handles cold enough to sting through our glove. We picked one up. A dog-shaped shadow rose from the corner where it had been sleeping, its wings folding down against crystal-tipped fur. It watched us with pale blue eyes and did not growl. It had known these knives. It had known the hands that carried them. The older fairy spoke from the hall. We had not heard her come back. "Put it down." We did. She stepped between us and the shelf. "Two students," she said. "A brother and a sister. They tried the spell together, thinking two wills could share the weight. The spell does not split. It picks one caster and burns the other out. She cast. He watched her freeze. He walked into the lake a week later." She looked up at the portrait, then at each of our faces. "You are not the first pair to think you are the answer. You are the second." She pointed at the door. "In the morning I send you to the lake tribe. They will refuse you too. Then you will go home." She left us. The hound settled at our feet. She and I did not argue. We understood, both of us at once, what the picture had been trying to say. Two wills did not make the spell safer. Two wills made a caster and a witness. One of us would burn. The other would carry it. We sat on the edge of the bed and looked at our shared hands, and for a long time we could not decide which of us was which in that story. Our body did not move, but this time the stillness was not a fight. It was the first thing we had agreed on since the snow: we could not attempt the spell the way the twins in the portrait had. We would have to find another way, or not cast it at all.

We slept on the floor beside the bed, not in it. In the morning the older fairy set two bowls of hot broth on the table and watched us drink. The winged hound sat at the door. The portrait of the boy and girl still hung above the empty pillows, and we did not look at it. She said, "I told you I would send you to the lake tribe. I have changed my mind about how." She laid the twin snowflake knives on the table between our bowls. "These belonged to them. Two blades, one pair. If you can throw them together and hit one mark, I will point you onward to a fairy at the lake who knows a path around the spell you want. If you miss, or if you argue, the hound carries you back to the tree line and you walk home." She tapped a knot in the far wall. A small circle, no bigger than a coin. "One throw. Each of you takes a knife. Both blades in the circle, or neither counts." We picked up the knives. The left hand took the girl's blade. The right hand took the boy's. He wanted to throw on a count of three. She wanted to breathe first and throw on the exhale. Our arms lifted and stopped. The old argument started under our skin, quick and familiar. Then I looked at the empty bed. She looked at the empty bed. The two children in the portrait had shared a spell and it had killed one of them because they had not truly agreed. They had only decided to try. "Breathe first," I said. "Then three." "Breathe first," she said. "Then three." We breathed. We counted. On three our arms moved as one arm. Both knives left our hands at the same instant and struck the wall a finger apart, inside the coin-sized ring. The handles hummed. The hound stood up and shook out its wings. The older fairy walked to the wall, pulled the blades free, and set them back in our palms. "Keep them," she said. "You earned the pair." She did not smile. "Follow the hound to the lake. Ask for Glacienne Frostwhisper. Tell her I sent you, and tell her what you learned in this house. She may know a way to cast the spell that does not require a witness. She may also refuse you. That will be her choice, not mine." We stepped out into the snow with a knife at each hip. The hound walked ahead, wings half open against the wind. Below the ridge, past a stand of black pines, a pale structure rose from the shore of a frozen lake, its spires clear as glass. She and I did not speak. We had thrown as one hand. It was a small thing, and we both knew it. The spell waiting for us at the lake was not a knife and a wall.

The hound brought us down through the black pines and stopped at the lake's edge. The ice stretched flat and pale to the horizon. Wind cut across it in long white ribbons. The pale spired house we had seen from the ridge was gone from view now, hidden behind a swell of drift and cloud. He said we should walk straight out. She said the wind would blind us before we crossed a quarter of it. The body froze on the shore. Our fingers were already stiff inside our gloves. "We can't stand here," I said. "We can't wander either," she said. "Pick a direction wrong and we die on the ice." The hound sat down. It had brought us to the shore and would go no farther. Then the air on our left went warm. Not a little warm. A full breath of summer against our cheek, wrong as a bell in a graveyard. We turned. A fire fairy stood on the frozen creek behind us, one boot on the pale ice, the other on a dark seam of running water beneath. The ice did not melt under him. His hair moved like a lit match. He carried no weapon we could see. "You're the twin," he said. "The old woman sent word ahead. I'm Blazen Emberwing. I was passing." He looked at the lake. "Nobody passes here. I lied. She asked me to walk you out." He said the tribe's house sat two hours northwest, invisible from the shore because the drift hid the spires until you were on top of them. He said the ice grew thin in three places between here and there, and he could feel them the way she and I felt each other. He held out a hand. His palm gave off heat like an open stove. "Walk behind me. Step where I step. If I stop, you stop." She wanted to accept. I wanted to ask why a fire fairy owed the old woman a favor. The body stalled again, one boot lifted, one boot down. Blazen watched us stall. He did not soften his voice. "Argue on the ice and you'll go through it. Pick now." We looked at each other, the way we had looked at the empty bed. Two wills, one body, and a thin road under our feet. "Behind you," we said together. We stepped onto the lake. The hound stood, shook out its wings, and lifted back toward the ridge. Blazen walked. We walked. Twice he stopped without warning and we stopped with him, and the ice under our next step gave a small dry crack we did not test. Two hours later the drift thinned and the pale spires rose out of it, close enough to touch. He pointed at the door and said, "Ask for her. I've done my part." Then he turned back toward the creek, and the cold closed over the place his heat had been.

The door of the pale spired house sat flush with the drift. We knocked once. Nothing answered. She knocked again, harder, and the sound went flat against the wood like a stone dropped in snow. I pressed an ear to the door. No footsteps. No voice. A row of small frozen shapes watched us from a shelf carved into the wall beside the frame — bunnies of clear ice, ears up, eyes bright. They did not move, but they were listening. She said Glacienne Frostwhisper was inside. I said Glacienne Frostwhisper did not care that we were. "We need to give her a reason," she said. "Then cast something," I said. "Small. Enough that she feels it through the wall." We drew the twin knives from our belt and set the points against the door. She wanted a frost sigil. I wanted a cold pull, the kind that draws breath out of a room. The body stalled the way it always stalled. Then heat came up behind us on the ice, wrong and sudden, and we turned. A fire fairy stood on the frozen creek at the foot of the steps. Not the one who had walked us across. This one was smaller, angrier, hair burning white at the tips. He said we did not belong at this door. He said the ice court had claims here, and he had been paid to keep the door shut. He threw fire. It came in a low sheet across the drift, and the bunnies on the shelf cracked from the heat, one ear falling, then another. We stepped back against the wood. Our gloves smoked. Then the sky above the spires split open with a beat of wings, and a hound came down onto the step between us and the fire — the same shape that had left us at the shore, or its brother, ice grown along its ribs and white feathers wide as a door. Behind the hound walked a man in white and gold, no older than a boy, his crown of ice sharp enough to draw blood. Angel Frostborne. He did not look at us. "Cast," he said. "I will hold him." He stepped past us onto the creek. The hound followed. Fire met ice on the seam of running water, and steam went up in a wall we could not see through. We turned back to the door. Two wills. One body. She said frost sigil. I said cold pull. Then we looked at each other and did not argue. We set both knife points to the wood and cast together — her sigil traced in my pull — and the cold went through the door like a hand. The door opened. A woman stood in the gap, small and gray-eyed, a cup of something steaming in her hand. She looked at the steam behind us, then at our knives, then at our two faces. "You cast that together," she said. "Come in. Quickly." We stepped inside. The door shut on the noise of the fight. Somewhere behind us, on the ice, the ice king was still holding the line.

The door shut behind us and the room was quiet. Glacienne Frostwhisper set her cup on a low table and looked from one of our faces to the other. Outside, muffled through the wood, we heard the hiss of steam where fire met the frozen creek. She said the fight would not last. She said the fire fairy on the ice had already sent a signal up the ridge, and more of his tribe would come before the hour was out. If they arrived while we were still learning, they would burn the door down and take us on the step. "You want the spell," she said. It was not a question. "Cast without a witness. Cast without burning one of you out." She wanted to know so. She wanted to know now. Glacienne shook her head. She said the spell could not be cast without a witness. But the witness did not have to be a second fairy. The witness could be a thing — small, alive, made of the same cold as the caster. She lifted a shelf's cloth. Three ice bunnies sat under it, clear-bodied, ears sharp, watching us the way the ones on the outer shelf had watched before the fire cracked them. "They hold what a second caster would hold," she said. "They break instead of you." She said we had one try before the door came down. She said we had to decide, together, which of us cast and which of us set the witness. The body stalled. She wanted to cast. I wanted to cast. Neither of us moved. Glass shattered somewhere above the door frame. A red line ran down the inside of the wood where heat pushed through. Glacienne did not look up. She looked at our two faces and waited. She said, quiet, "He cast." I said, quiet, "She casts." We drew the twin snowflake knives and set one in each of our hands. She took the blade. I took the bunny from the shelf and set it on the table between us, ears up. She began the spell. I held the witness. The cold came up out of the floor and into our shared chest, and I felt it try to climb into her head and mine at once — then it caught on the bunny instead, and the small clear body went white from the inside. Her hand shook. Mine did not. The bunny cracked once, straight down the spine, and fell into two clean halves on the wood. She finished the shape of the spell. The red line on the door went black and cold. Glacienne picked up the two halves of the bunny and set them in her palm. "You have it now," she said. "Once. You cannot do it again with this one." Above us, on the roof, we heard the first pair of boots land in the snow.

The two halves of the bunny sat in Glacienne's palm. Above us, boots pressed on the roof and slid toward the eaves. A second pair landed. Then a third. Glacienne set the halves down and told us the spell was in our body now, but a spell held once was not a spell owned. We needed to cast it again, clean, without a witness to break for us. We could not do that here. Not with fire on the door. She wanted to fight through them. I wanted to run. The body stalled at the table. Glacienne watched us stall and did not wait long. She said if we stayed, the house burned with us in it. She said Angel could hold the front for a count, no more. The door shook. Angel Frostborne stepped in from the side room, white coat still bright, one sleeve scorched black at the cuff. His hound came behind him, wings folded tight. He looked at our two faces and spoke plain. "Back door. Creek path. I take the front. The hound takes your flank." He did not wait for us to answer. He turned and walked toward the shaking door. Glacienne pushed us toward the rear of the house. She pressed the twin snowflake knives back into our hands, one in each. She said the creek ran under a thin shell of ice past the yard, and the fire fairies would not follow onto it. She said their leader was not stupid. Their leader would call them off the ice before he lost a second one through it. We went. The back door opened onto pale flat stones and the winding creek beyond. The hound moved at our left. Behind us, the front door cracked and Angel's voice cut once through the noise, short, ordering someone back. We did not turn. She wanted to turn. I wanted to run. For once we agreed on the second thing and the body moved. We reached the creek and stepped onto the shell. It held. Three fire fairies broke around the corner of the house and stopped at the bank. Their leader came up behind them, red hair bright against the snow, and lifted one hand. Blazen Emberwing. He looked at us across the ice and did not throw fire. He said one word to his fairies and they stepped back from the edge. He watched us go. His mouth moved once, like he wanted to say something more, then closed. The hound crossed with us. We walked until the house was small behind us and the noise thinned to nothing. On the far bank we stopped and let the body breathe. She said we should have stayed. I said we are still alive. Then we said, together, that the spell was ours now, and we had to cast it clean before the lake. That was the next thing. The creek carried the sound of the fight away.