Who had actually set the trap for Sherzal was open to debate. Nona had used her thread-bond with Ara to ask her to do it. Ara, too weak to set the wires, had used that same bond to inhabit Nona’s body while Nona in turn inhabited Ruli and spoke with Sherzal behind the blast doors. The bloody lengths of Ark-steel would be returned to the wire kit that Kettle had given Nona along with the poisons and cures carried by every Grey Sister.

Even so, it was Ara’s task to pull the wires from Sherzal’s gory remains.

‘Go with her, Clera.’ Nona nodded and motioned the two of them back into the corridor. Ara would need support.

When the way was clear Nona would let Sherzal’s guards go. Joeli would stay here. Jula had tied the girl with Safira’s cords. Joeli might be good with threads but Jula tied better knots.

‘The book was a lie?’ Ruli came closer, cradling her injured arm as if it were made of eggshell. Jula hovered around her, trying to help. ‘I went through all that for nothing?’ Now that Nona had set the Noi-Guin shipheart against the far wall with the Sweet Mercy shipheart both novices could approach her.

‘Maybe not a lie,’ Nona said. ‘Perhaps just misguided and unnecessary. What was important was that you believed its value. That’s what got us in here and what kept you both alive. It was always Abbess Glass’s intention that the book would be the key that got us to the door of the Ark. I don’t imagine she knew it would be with the Scithrowl fighting in Verity’s streets.’

‘So how do we control the moon, if we could even get in there? Which we can’t,’ Jula asked. ‘Aquinas’s instructions are very complex … If they’re wrong then I don’t know what to do.’

‘Well. The first thing to do is to open the door, no?’ Nona tried to shut out the voices of her devils as they raged against Jula’s stupidity. If the girl came any closer Nona might just reach out in an unguarded moment and end her. She leaned back against the wall. ‘Before that though … I need this fucking knife out of my leg!’

Jula flinched as Nona’s voice rose to a shout, or perhaps at the cursing, or both. Even so she came forward, already unbinding her habit cord to use as a torniquet. Nona put her head to the wall and ground her teeth while Jula set to work.

‘How can we open the Ark?’ Ruli asked. She had a right to ask. She had had envenomed needles driven under her fingernails.

‘I—’ Nona roared as Jula drew the cross-knife from the back of her thigh and tightened her habit tie above the lacerated muscle.

‘Nona!’ Clera came back in, trailed by Ara, pale-faced and bloody-handed. ‘Are you …’

Jula stood up, tossing the little knife to the floor. ‘She’ll live.’

Nona turned her black-eyed stare on Sherzal’s guards. ‘Out!’ She snarled the word through gritted teeth. ‘Join the defence if you want to survive the night.’

Clera spotted Joeli, sitting bound on the floor. ‘I know her. One of Sherzal’s creatures.’

Nona bit back on the accusation that Clera was nothing more than that herself, and tried to drive the devils from her tongue.

‘We should get the truth out of her,’ Clera said, ignoring Jula and Ruli’s staring. ‘Sherzal didn’t have all her eggs in one basket. She was only going to share with Adoma as a last resort. She was after more shiphearts of her own. I know that much. She had an agent among the ice-tribes and she’d set her hunting down Old Stones. You really don’t want to know who I heard it was … But rich girl here, she knows for sure.’

‘Nona!’ A call from Ara at the doorway.

Out in the corridor a fierce light had overwhelmed the ambient illumination. It glared from the doorway of the chamber that held the travel-ring. The blaze made harsh silhouettes of the guardsmen now frozen a few yards from it. A deep throbbing buzz trembled through the ground.

Nona drew her sword. Ara struggled to draw her own. Clera’s blade cleared her scabbard with a hiss.

A crack rang out, like the world ending, and the light died. At first Nona could see nothing. Afterimages filled the corridor, swimming across each other. As they faded and the dark shapes of Sherzal’s men reasserted themselves Nona saw that a new figure stood there ahead of them, and in her hands burned two balls of light, one a virulent green, the other the red of iron just starting to glow.

‘Yisht!’ A scream from Joeli behind them.

‘Oh hells …’ Clera’s blade wavered, the point dropping.

Nona blinked away the remaining traces of her blindness, and there, alone in the corridor now as the guardsmen ran off in terror, stood the ice-triber, so thickly patterned in devils that no patch of unstained skin showed.

I cannot die. Yisht’s last words and Raymel Tacsis’s too. Perhaps if the black ice taught any lesson it was that evil never truly dies …

‘Nona?’ Yisht’s smile twisted. A moment later the rest of her rippled and in her place stood Zole, her face tight with strain.

‘Zole?’ Ara gasped. ‘You’re dead!’

‘She’s playing games with our minds!’ Clera backed a few paces.

‘With two shiphearts in my hands I could make you see anyone I wanted to,’ the figure said. ‘But I am Zole.’

‘She’s lying,’ Ara said. ‘Zole died.’

‘No,’ Nona said. ‘It’s Zole.’

And as she said it Tarkax Ice-Spear stepped out into the corridor, ten yards behind his niece and wincing as if he stood too close to the heat of a fire. Zole continued her advance and others of Tarkax’s tribe emerged, pushing at his shoulders.

The guards already ran off. As Zole drew closer Ara and the novices backed into the chamber. Even Nona couldn’t endure the combined pressure of both shiphearts.

‘How is she here?’

‘You knew? You lied to us?’

Nona shook her head. ‘I promised Abbess Glass. Zole did too.’

When Nona had returned alone with the shipheart she had reported to Abbess Glass immediately. On the abbess’s instructions she had let them all believe Zole to be dead and had made no mention of Yisht. Somehow the absence of any mourning among the novices had deepened Nona’s affection for Zole. The girl walked a lonely path and she walked it without complaint or compromise.

Nona hadn’t heard from Zole again for nearly two years and when she did it was to discover that they were thread-bound. Somehow during their long escape from the black ice, when Zole carried her half senseless from that freezing hell, the ice-triber had forged the bond between them.

At Abbess Glass’s suggestion Zole had set herself the task of bringing to the empire both of the shiphearts controlled by her tribe. At the same time, and seemingly at her own behest, Zole had set to convincing the emperor’s sister that Yisht still lived and was attempting exactly the same thing – to bring Sherzal the two shiphearts she needed. All those years ago Abbess Glass had seen the pieces before her and set them in motion. Tarkax Ice-Spear’s ambition to protect the tribes by keeping the Corridor open was just one more factor to wrap into the long game. Quite how she knew where the cascade of cause and event would lead Nona had no idea, but the abbess had always made it her business to know things. Nona had seen the results: the application of knowledge could unlock doors that her flaw-blades couldn’t so much as scratch, and it could bring down those so mighty that no feat of arms would stay their hand.