At the exact same moment, Princess Anya Phoebe Cornelia Argen of the Island of Dousha, Duchess of the Silver Mountains, Countess of the Winged Forests – dirt in her fingernails and blood on her lip – darted over the rooftop of her castle. A dozen royal gaganas flew overhead, following her. It was dusk, and the gold beaks of the gaganas caught the moonlight and sent it skittering across the stone.

There was a movement in the darkest corner of the rooftop. Anya froze, and whisper-hissed, ‘Who’s there?’

But it was only Coren, a young gagana, scarum-feathered and confident as a king. He came skimming up to land on her shoulder. ‘Quick. He’s coming up the stairs.’

Anya’s bedroom was in the far corner of the West Wing: you could slide sideways out of the window on to the battlements, and from there look out across the stately gardens, down over the rooftops and clamour of the city, to the ocean where the winged unicorns bathed.

But Anya was not there that evening for the view. She was there to stop a death.

It was Gallia who had warned her. The old bird had come flying in through her bedroom window just minutes earlier, croaking in a high panicked urgency Anya had never heard before. ‘The egg! Anya! He’s coming for her egg!’

A guard in the grounds – a stranger, a man Gallia had never seen before – had shot a gagana with a crossbow. It was unheard of – royal gaganas were protected by law.

The soldier had nodded in satisfaction and had turned to his companion: ‘Get the egg then. It’s what he’s paying us for.’

Who would want a gagana egg badly enough to kill for it? It was unthinkable! The gaganas were not just birds; they were her best friends and dearest companions. They were as wise as any human – much wiser than most, Anya thought. In a castle built on rules and regulations, they filled the air with light and song and the clamour of wings.

The egg belonged to Felin, whose body now lay limp, out of sight by the castle lake. Anya did not know Felin well, but she knew her nesting spot: on top of a chimney for warmth, on the far side of the West Quadrangle.

Crouching low, she ran as fast as she could along the courtyard side of the slanting rooftop. She had never run it before, and her stomach swooped as her feet fumbled for purchase.

‘Take care,’ said Gallia. The old bird flew just above her head, and came now to rest on her hair. ‘The slate!’

Too late. Anya set her foot on a loose tile, and she lurched as it dislodged and dropped to the ground with a crash. But she had not been drilled for endless hours in posture for nothing. Anya Argen could pirouette with a book on her head; her balance was strong and true. She caught herself and dropped to a crouch.

‘Hurry!’ called Coren. ‘He’s close!’

Anya scrambled onwards, and the egg was there: small, silver-white, delicate as blown glass. She took it as if handling the world’s most precious porcelain, and her heart surged with relief. She turned to run back to her room.

The trapdoor in the roof shifted, creaked, began to lift.

With a low cry, she dropped to her stomach, pressing herself against the stone. The shadow covered her, but it wasn’t enough. She would be caught. He would take the egg from her.

The trapdoor lifted. Anya swore. The soldier’s face appeared, scanning the rooftop.

Anya waited until his whole head was clear of the trapdoor. Then she cried out, ‘Coren! Attack!’ Coren gave a high shriek and dived straight at the man’s eyes. The man bellowed in shock.

Anya cried, ‘Together! Now!’ and every gagana around her rose in a cloud, and cannoned towards him. He roared, and ducked back down behind the trapdoor – and Anya ran, one hand clutched to her chest with the egg, back to her room.

She crouched on her bed and feverishly checked every inch of the shell. It was uncracked, unharmed.

Anya held the egg close, breathing on it to warm it. She would tell her father, she thought, as soon as he was free of his royal duties. He loved the gaganas. He would know what to do. He always did.

Her fingers went to her pendant: a small silver disc on a chain. Her mother had left it to her when she had died ten years ago, and Anya never took it off. Touching it gave her comfort; when she was a baby she had cut her teeth on it. Now she put the edge in her mouth, and bit gently down on it.

Something was bitterly wrong in Argen Castle. This was fresh proof of it…