Tab realised with a start that the morning was passing. She glanced at the scroll in her hand. There was no way she would get far in the Navigators’ Guild if she couldn't even deliver a letter on time.

She headed for the Naval Headquarters, located in and around the mainmast. She made her way hurriedly to the Square of the People, dodging market stalls and managing to buy nothing, which wasn't hard, especially when the vendors saw her apprentice's tunic. Everyone knew how poorly paid apprentices were.

Tab reached the imposing sculpted entrance of the Naval Headquarters, and stopped as she always did to look up. Rising straight and sheer above her, the massive polished trunk of the mainmast – en crusted here and there with barnacle-like dwellings, protuberances and walkways – rose to a dizzying height. The section known as ‘uppermost’ was just a vague shape lost in misty cloud.

Tab gulped, and hurried inside. A moment later…

Uh-oh, she thought as she swept through the doors of the despatches department.

The Archon's nephew, Florian Eftangeny, was on duty. Tab bit her lower lip. She had won her job as Quartermaster Dorissa's personal clerical assistant fair and square, but Florian had been next in line and the Archon's nephew hated her for it. To be beaten by an ex-Dung Brigader!

‘Running little errands, are we?’ sneered Florian, eyeing the scroll in her hand. His slug-like upper lip curled scornfully. ‘Haven't really advanced very far, have we?’

Tab flushed. Florian, a short, plump boy with a moon-shaped face, sour expression and receding hairline, always managed to hit a nerve with Tab. It was as if he could read her mind – or her fears.

Florian snorted. ‘Put it over there,’ he said, pointing languidly to an in-tray.

‘It's to be hand-delivered to First Lieutenant Crankshaft immediately,’ Tab said firmly.

Florian smirked. ‘Is it now? Well I'll deliver it myself then.’ He fingered the jewelled dagger in his belt. All the children wore daggers these days, just as all the adults wore swords. Times were uncertain. ‘Put it in the in-tray and get out of here. I've more important matters on hand than to talk to a witless rift girl.’

Stung, Tab nevertheless dropped the scroll in the in-tray. Such scrolls were usually urgent communiques between navigators and sailors. If Florian failed to deliver it within a set time, she would get into trouble. And that was all she needed.

‘You'll remember it's there?’ Tab pressed.

Florian didn't bother to look up.

Tab slept uneasily that night, tossing and turning. Finally she woke, drenched in sweat. Taking a cool drink of limewater she lay back down, staring at the ceiling. Maybe she should have insisted on delivering the scroll to the first lieutenant. But no, there was no way she could have. Clerical assistants weren't allowed upside. And she couldn't make that idiot Florian do anything. He was almost as useless as his uncle, the Archon.

Tab tried to go back to sleep, but couldn't. Almost at once she was conscious of a feathery sensation in her mind. She had felt it many times this past year. Knowing what was about to happen, she tensed, frightened. And with a sickening lurch, she found herself in a dungeon.

She was low down, close to the floor. In her immediate field of vision were flagstones slick with scum, some large metal poles, and a snout from which whiskers jutted. She was seeing with the eyes of a rat. To some extent, she also felt the rat's awareness. The rat was hungry. It had been searching for food for some time now. The sound of water dripping sporadically came to it. Then a scream.

The view froze. The rat, sitting in shadow, did not dare move. There were more screams, hopeless and high-pitched, as if a child were being hurt. Tab's heart ached for the screams’ owner. The rat started to edge back into deeper shadow.›››No›› The other way – find out what's happening!

Tab had no idea of what she had done, but suddenly – back in her room, Tab gasped – the rat obeyed. Tab felt a dizzy excitement. Was she actually controlling the rat? Or had it just decided to investigate the noises itself? That seemed unlikely.

The rat scuttled forward, darting between the metal poles which Tab now realised were the bars of a cell. It crossed a passageway and nosed in between more bars, edging along the wall and into the shadows cast by a bunk bed.

A youth and two men, all with cruel faces, occupied the cell. One was torturing a small boy with a pale, freckled face and sandy-coloured hair. The boy, who must have been about eight years old, screamed again. His face was wet with tears and his upper lip and chin were covered with snot.

‘Where is the icefire?’ demanded one of the men. At a nod from the questioner, a brute of a man tightened a knotted rope around the boy's throat. ‘What did you say?’ the interrogator demanded. ‘Speak up!’

Tab was breathing heavily. An uncharacteristic anger was building up. She could tell from their livery that they were Tolrushians, but how could the enemy be on board Quentaris?

Tab now saw the main speaker more clearly. He was a boy of about fourteen, but dressed in rich clothes. He had a crafty look about him. ‘We know your people have icefire,’ he snarled, ‘and we will have it from them!’

The victim whimpered. Tab could see that he was very, very scared.

The torturer tightened the rope. The boy choked, and fainted. The boy-leader scowled. ‘Leave him for now,’ he said, spitting on the straw-strewn floor. ‘There are other matters at hand – prey, for instance.’

One of the men cleared his throat. ‘You still mean to attack, then?’

‘I do.’

‘Is that wise, m'lord, when our own icefire fuel is so depleted?’

The boy-leader stopped at the door, eyeing his advisor. ‘There is more than one source of icefire, Genkis. There is also the matter of revenge.’

The boy stalked out of the cell. No one noticed the rat watching from the shadows.

Abruptly Tab's vision lurched again. This time she was wheeling through the sky. On either side, great bat-like wings slowly flapped. The view banked hard, and into her line of sight swept something that left her stunned.

Floating in dense cloud was a city.

Above it stretched enormous sails, torn and tattered and filthy. A grim castle bulged from the port side prow, and huge grappling arms like crab claws projected forward on either side of the bowsprit. The whole thing had an evil look. Like a sky pirate's ship. Or a man-o’-war.

Tab had never seen such a place, but she recognised it immediately.

Tolrush.

It couldn't be, but it was. Tolrush had become a flying city, just like Quentaris. And slowly it dawned on Tab that Fontagu had inadvertently pulled Tolrush into the spell so that the two cities had, in that moment of Rupture, been magically joined. What had happened to one, had happened to the other. And who knew what other cities had also been ripped into the vortex?

Tab's heart thudded with sudden realisation. Judging by what the boy-leader had said, the Tolrushians blamed Quentaris for their misfortune.

Which could only mean…

Tab sat bolt upright.

She dressed hurriedly and ran as fast as her legs could carry her to the Navigators’ Guild headquarters. She didn't stop at the gates. A guard yelled a warning and she felt an arrow hiss swiftly past her shoulder. Angry shouts followed. She ran faster.

Breathless, she skidded to a stop outside the operations room. By now alarms were clanging. The doorway opened suddenly, revealing several guards.

‘Gotcha!’ someone snarled from behind. Tab was whisked off her feet.

‘Put her down,’ said a calm voice.

The guard dropped her and Tab went sprawling. When she looked up she saw a navigator staring quizzically down at her. She's scanning me – seeing if there's any danger, Tab realised.