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  Copyright © 2026 by Clíodhna O’Sullivan

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  Cover design by Theresa Evangelista

  Design by Jim Hoover, adapted for ebook by Michelle Quintero

  Library of Congress Cataloging-in-Publication Data is available.

  First published in the United States of America by Viking, 2026

  ISBN 9798217040506

  Ebook ISBN 9798217040520

  The authorized representative in the EU for product safety and compliance is Penguin Random House Ireland, Morrison Chambers, 32 Nassau Street, Dublin D02 YH68, Ireland, https://eu-contact.penguin.ie.

  prhid_prh_7.4a_155406395_c0_r1

  Contents

  Dedication

  Irish Pronunciation Guide

  Map of Domhain

  Content Warning

  Part One: Ailm’s Keep

  Chapter 1

  Chapter 2

  Chapter 3

  Chapter 4

  Chapter 5

  Chapter 6

  Chapter 7

  Part Two: Lambay, First Island

  Chapter 8

  Chapter 9

  Chapter 10

  Chapter 11

  Chapter 12

  Chapter 13

  Chapter 14

  Chapter 15

  Chapter 16

  Chapter 17

  Chapter 18

  Chapter 19

  Chapter 20

  Chapter 21

  Part Three: Lambay, Second Island

  Chapter 22

  Chapter 23

  Chapter 24

  Chapter 25

  Chapter 26

  Chapter 27

  Chapter 28

  Chapter 29

  Chapter 30

  Chapter 31

  Chapter 32

  Chapter 33

  Chapter 34

  Chapter 35

  Acknowledgments

  Appendix: Image Description

  About the Author

  _155406395_

  For Conor,

  Maya-Rose,

  Éanna

  & Aodhán

  Most of the names in Her Hidden Fire are variations on Irish names; some are derived from an ancient Irish tree-based alphabet known as Ogham. Below is a rough guide to the Irish pronunciation.

  Domhain

  Dow-in (“world” in English)

  Ailm’s Keep

  Ailm – Al-im

  Family castle north of the Blackstairs, the large mountain range in northeast Domhain

  Éadha – Eh-ya

  Ionáin – Yun-aw-in

  Aedan – Ay-dan

  Úra – Oo-ra

  Béithe – Bey-he

  Huath – Huw-ath

  Ferne – Fearn

  Jarlath – Jar-lath

  Treasa – Tra-sa

  Magret – Ma-grette

  Lambay

  Lambay islands—a group of three islands off the east coast of Domhain, named First Island, Second Island, and Domhain’s Eye

  Apprentices—Channeller

  Senan – Se-nan

  Linn – Linn

  Coll – Coll

  Cormac – Cor-mack

  Eoghan – Owe-an

  Apprentices—Keeper

  Gry – Gry

  Ailbhe – Ale-va

  Síofra – Shee-fra

  Cara – Car-ah

  Muir – Mwir

  Béibhín – Bey-veen

  Nuala – Noo-la

  Sibéal – Shib-ale

  Síle – Shee-leh

  Masters

  Dathin – Daw-hin

  Irial – Ir-ee-al

  Cathal – Coh-hul

  Joen – Joe-en

  Ruadh – Roo-a

  Odhran – O-ran

  Head Keepers

  Fiachna – Fee-ach-na

  Maebh – Mayve

  Fodder

  Seoda (also known as Donn) – Show-da

  For a plain-text version of this image, go to this page.

  Please note this book includes references to coercive behavior and sexual and physical assault.

  Part One

  Ailm’s Keep

  1

  Behind the great castle known as Ailm’s Keep, there was no more than a suggestion of daylight when a black-clad figure appeared, racing toward its East Tower.

  She halted at a massive oak tree near the tower and pulled herself up onto its thick branches; they were still bare and would be for weeks yet. The spring thaw had only just begun. Around her the air was filled with the roar of meltwater pounding down the mountain stream behind the Keep into the small lake just past the oak tree. The thick ice that’d gripped the lake all winter long had shattered overnight, leaving small white islands bobbing and turning in the water. Éadha was glad of the water’s roar, masking any sounds she might make. With her cloak tied back over her shoulders to avoid snagging and her cloud of dark hair tucked inside her hood, she climbed swiftly up through the branches.

  Soon she was level with the high wall along the Keep’s central courtyard. Even though it wasn’t quite dawn, already she could see figures moving about below, stable lads lighting fires in big iron braziers to burn off the chill in the air for the crowds arriving later. The courtyard wall was narrow, only just wide enough for one person to balance on top of. Spreading her arms out wide like a dancer and with a small prayer no one would look up, Éadha began inching along over the weeds that’d seeded themselves in cracks. Her foot slipped on a dandelion root and she fell into a wobbly crouch, grabbing the top of the wall with her hands to stop herself falling, while one leg dangled over the long drop.

  “Bugger,” she muttered, her heart skittering as she eased her leg oh-so carefully back up onto the wall until she could stand again. The wall ended at the side of the East Tower, and she reached it just as the sun broke free of the horizon. It was going to be a clear day.

  Above her was a stone window ledge. She could just reach it if she leaned out and didn’t think too much about what’d happen if she missed. She caught at it, first with her left hand, then, swinging her legs out into space, with her right, offering up her thanks there hadn’t been a Channeller in Ailm’s Keep for the past quarter century to keep its walls whole. It meant there were cracks in the tower wall deep enough to wedge her toes into and push up; she got one elbow over the ledge, then levered the rest of her body up until she was crouching on the narrow stone lip.

  The window in front of her was made of dragonglass, the thick, wavy glass formed when a dragon burned the far sands of Westport, where the Channellers fought their endless battle to hold them back from Domhain’s mainland. Through the glass was a large bedroom with stone walls hung with tapestries of the great Channeller battles. To the right, the embers of a fire glowed in a slate fireplace, casting a golden-red glow over the room. Directly in front of her stood a large four-poster bed with a worn velvet cover, perfectly smooth and clearly not slept in. At the end of the bed sat a young man of about seventeen or so. He was already dressed in a cambric shirt of fine white linen and dark pants. His elbows rested on his knees as he stared into the dying fire, while his tawny, tangled hair stood on end, as if not too long ago he’d been pushing his hands through it. Éadha stared in at him for a moment, her expression unreadable, then rapped once on the glass.

  Ionáin turned his head at the sound, looking wholly unsurprised to find a tall, hooded girl dressed in black crouched at his bedroom window. Standing with a small stretch, as if he’d been sitting still a long time, he crossed the room to swing open the latch.

  “Hey,” he said, turning away again.

  “Hey,” said Éadha, easily swinging herself in through the window and sitting down on the ledge, as if she didn’t feel entitled to come any farther in. The window was high off the ground, so that at full stretch, her long legs in their battered leather boots only just grazed the floor. Lowering her hood, she gripped the window ledge, tense now as she watched Ionáin. He’d gone to stand in front of the fire. To his left, on a rosewood stand, hung a set of long, heavy robes embroidered with gold thread and embellished with precious stones. His Reckoning robes.

  “Did you sleep?” said Éadha quietly.

  “Nah. No point even trying. Y
ou?”

  Éadha shook her head while Ionáin cleared his throat before going on. “I’ve had an idea though.”

  “Oh yes?” said Éadha.

  “How about if I just tell them—my Family and all those Masters and Channellers downstairs right now—that it’s a bit unfair, really, to reduce my entire existence to whether I have this one mystical ability, here in my head.” He tapped his temple before looking across at Éadha with a small smile. “Then they might reconsider all this?”

  He gestured toward the ornate robes and past them to his bedroom door. Beyond it, they could already hear the sounds of the Keep coming to life.

  Éadha gave a small snort of unwilling laughter. “Do I think that if you point out to those old men downstairs that their precious centuries-old Reckoning ritual is in fact ‘quite mean,’ Master Dathin will slap his forehead and say, ‘You’re so right, let’s just cancel the whole thing’?”

  “Well, yes,” said Ionáin, a grin breaking across his face as he looked at her. “I mean, I do have other good qualities.”

  “Such as?” said Éadha, her voice teasing now.

  “Have you seen me with kittens? Not to brag, but I’m fairly sure I’m the world’s best kitten wrangler.”

  At this Éadha laughed out loud before leaning back against the window and folding her arms. “Ah, well then, absolutely. They’ll probably thank you for pointing out the cruelty of their system, tell your Family they can hang on to the Keep regardless, maybe channel some repairs, and be gone by lunchtime.”

  They both chuckled, though it only lasted a few seconds before trailing away, their hearts not really in it. After all, the stakes were too high on this, Ionáin’s Reckoning day. The day he turned seventeen and the day he’d finally find out if he had the ability to channel magic or if instead he—and his Family—would lose everything. His father, Aedan, had failed his Reckoning a quarter century earlier, and the rule was ironclad. If two successive generations of a Family failed their Reckonings, the gift was deemed to have died out in their bloodline and the Family was disavowed.

  Silence descended between the two of them, broken only by the soft whump of ash collapsing in the grate and throwing out sparks. Éadha felt all the tension return to her body.

  Ionáin, meanwhile, stuck his hands out in front of him and said, “I can’t seem to stop them from shaking. I’ve been trying, you know, all last night.” He looked up at her, and this time the simple anguish in his eyes twisted her heart—the shared knowledge that in the next few hours he’d either be the savior or the damnation of his Family, and he had absolutely no control over which it’d be.

  “It’s funny,” he went on. “I’m almost as worried I’m just going to embarrass myself when I walk out there in front of everyone. I’ll stutter or, I don’t know, trip over those stupid robes.”

  “You won’t though,” said Éadha. Ionáin turned to look directly at her, his eyes a midnight blue in the firelight.

  “I missed you, you know, last night. I wish you still slept there.” He nodded toward the fireplace and the rug where she’d slept on a makeshift bed for years. An orphan since early childhood and raised by her uncle, a Keep herder who spent long weeks on the mountains, she’d become Ionáin’s scáth, his shadow. Stationed in his room at night since they were both eight years old so his mother, Lady Úra, could focus on nursing his older brother, Dara, through one illness after another. Until he’d died two years ago, aged sixteen, not long before his own Reckoning, when a bout of influenza swept through the Keep, leaving Ionáin as the Ailm Family’s last surviving heir, their last hope of keeping their title and their home. “It would’ve made it easier to get through.”

  Éadha slid down from the window ledge, crossing the room to stand beside him in front of the fire. So close together, they were a study in contrasts. Ionáin with the mop of tawny-gold hair he’d inherited from his mother’s side, his face drawn and pale from lack of sleep, the shadow of stubble on his jaw. Éadha’s heart-shaped face was framed by her cloud of black hair while her honey-brown skin was still flushed from her climb earlier. Growing up, she’d always been the taller one, though he’d caught her in just the last few weeks—a thing she still wasn’t used to. It meant their eyes were level now as she fixed him with a fierce stare and said, “You know you don’t have to do this. Play their stupid game. You, me, out this window. We’d be into the forest and across the Steps before anyone knew you were gone.”

  “Again with this?” said Ionáin.

  “It’s a good idea. And I’m persistent,” said Éadha.

  “Yes, but you also know why I can’t do it,” said Ionáin.

  She did. If he ran, his parents would be condemned as the family of a cowardly traitor who couldn’t even face his own Reckoning. At least if he stayed, even if he failed, he’d have proven his Family’s loyalty. He and his father would still be sent to Westport to face the dragons, the fate of a failed bloodline, but it left open the chance his mother’s powerful brother, Lord Huath, might take pity on her and let her live out her days in some corner of his lands.

  The two of them were standing so close together now their shadows on the wall behind them seemed to merge, waving and flickering in the firelight.

  Staring at Éadha, Ionáin’s voice deepened as he went on. “But, Éadha, if I fail today and Huath takes over, you’ll need to run. Promise me—”

  He never got to the end of that sentence because as he spoke, his bedroom door swung open. The two of them sprang apart. In the doorway was Béithe, the white-haired housekeeper and Ionáin’s old nurse, balancing a tray filled with food. She marched past the pair of them to set the tray down on a low table by the window.

  “At least you’re half-dressed, young sir,” she said, her voice tart. “But you might want to get the rest of the way there before your mother arrives in with the multitudes, looking to get those robes on you.” She turned to look at Éadha. “As for you, young one, you’ll have to get yourself out the way you came in before Lady Úra gets here. On with you now, and mind you come back in through the kitchen like a normal person. Magret’s looking for you.”

  Éadha knew Béithe was right. That, unbelievably, after a lifetime waiting for this day, their last moment had passed and there was no choice now but to face what had to be faced.

  Still, though, she hesitated, turning back toward Ionáin. He was bending to pick up his tunic from the floor and didn’t see the look that came into her eyes as she said, in a voice far more urgent than before, “Ionáin, listen. There’s something I need to…”

  But whatever it was she wanted to tell him went unsaid as Béithe caught Éadha by the arm and hustled her back to the window.

  “No. No more chat, young one. The time for that is gone. He’s to get ready now, and you’ve to go get yourself in position. On with you now.” Éadha had no option but to go out of Ionáin’s window and climb back down the way she’d come.

  Her last sight of Ionáin, as she lowered herself from the ledge, was of him approaching the heavy robes with his shoulders straight and squared, like someone getting ready to march to their own execution.

  By the time she reached the courtyard, it was already overflowing with people from the local village. As was the way for Family Reckonings, the whole village had been invited by Ionáin’s father, Lord Aedan, to bear witness to his son’s trial. They milled about, men and women stiff in their best clothes, shushing their children as they dashed across the cobblestones, squealing excitedly. The older men had clustered around the bonfires burning brightly now in the deep braziers, murmuring quietly as they warmed their hands on the flames.

  Just as Éadha reached the kitchen door, a head poked out. It was Magret, the choirmaster. “Éadha!” she said, her voice exasperated. “Where’ve you been? I swear you’d be late for your own funeral. Come on.”

  Éadha said nothing, only following Magret in. The kitchen was in an uproar, the wooden tables piled high with food, servants running in and out to reload silver platters with force-grown fruit and refill carafes with channeled wine. Because the Ailm Family hadn’t had a Channeller since Ionáin’s grandfather’s time, it’d all been brought in specially for the Reckoning on carts from the white marble city of Erisen, across the plains of Rath and over the Blackstairs Mountains that separated Ailm’s Keep from the rest of Domhain. The journey took weeks, but as the Family had no way to channel crops or force-grow fruit of their own, they had no choice.