After the noise of the other world, the silence surrounding him here seemed even more unreal than the Heinzel. It always took his eyes a few moments to adjust to the darkness. The lights of the other world made forget how dark nights here could be. Jacob looked around. He needed a place where the bottle’s occupant wouldn’t grow all the way into the clouds. And Jacob couldn’t risk any damage to the tower, and the mirror inside.

The old chapel.

Like the tower, the chapel had been left untouched by the fire that had destroyed the castle. The building lay just beyond where the overgrown garden stretched down the slope of the hill. Jacob had to hack a path through it with his sabre. Mossy steps, crumbling statues, marble fountains filled with rotting leaves. A few headstones still stuck out from the unmowed grass: Arnold Fischbein, Luise Moor, Käthchen Grimm. The servants’ graves had been spared by the fire, while the mausoleum of the castle’s owners had been reduced to a circle of sooty stones.

The wooden doors of the chapel were so warped that Jacob barely managed to open them. The inside looked desolate. All the colourful glass windows were broken, and the wooden pews had long gone to heat a few draughty cottages. But the roof was still intact, and the nave was barely more than twelve feet high. This would have to do.

A Thumbling peered over the rim of the dried-up font as Jacob pulled the leather sheath off the bottle. The brown glass was so cold that it nearly burnt his fingers. Its occupant was not from the south, where Djinns could be found in the markets of every desert village. The medicine Jacob needed could be provided only by a northern Djinn. They were very rare and very vicious – which explained why the men who hunted them were often even more scarred than Chanute. The spirit Jacob was about to set free had given his captor such a fight that the man had died within hours of trapping it. Jacob had buried him himself.

He chased the Thumbling outside before his curiosity cost him his life. Then Jacob closed the doors.

‘They are all murderers, Jacob, never forget that!’ Chanute had warned him more than once about the northern Djinns. ‘They get locked up because they love to kill. And they know they have to spend the rest of their immortal existence serving every fool who gets hold of their bottle, so their only desire is to kill their master and take possession of the bottle themselves.’

Jacob stepped into the centre of the chapel.

The etched pattern on the neck of the bottle was what bound the Djinn inside. Jacob copied it on to the palm of his hand before he drew his knife. The only thing more dangerous than catching one of these spirits was letting him out again. But what did he have to lose?

The seal on the bottle was that of the judge who’d sentenced the Djinn to an eternity behind brown glass. Jacob used his knife to peel the wax off the top. Then he set the bottle on the flagstones and quickly stepped back.

The smoke that rose from the mouth was silvery-grey, like the scales of a fish. The wisps formed fingers, an arm, a shoulder. The fingers felt the cold air and clenched into a fist. From the shoulders grew a barbed neck like a lizard’s.

Careful, Jacob!

He ducked into the smoke still rising from the bottle. Above him, a skull with a low forehead and stringy hair was taking shape. A mouth opened. The groan it uttered made the chapel shudder like the haunches of a frightened animal. The cracked windows burst, and Jacob breathed the dust of broken glass. Coloured shards rained down on him while the spirit above him opened his eyes. They were white, like the eyes of a blind man, and the pupils were like black bullet holes. Their lurking glance found Jacob just as he got hold of the bottle and closed his fingers firmly around its neck.

The huge body ducked like a cat ready to pounce.

‘Will you look at that!’ The Djinn sounded hoarse, as though he had lost his voice in his glassy prison. ‘And who are you? Where’s the other one, the one who captured me?’

He leant down towards Jacob. ‘Is he dead? I remember breaking his ribs. But that is nothing compared to what I will do to that judge. I’ve been picturing it all these years. I will pluck him apart like a flower. I will pick my teeth with his bones and blow my nose on his skin.’

His hoarse rage flooded through the chapel, and the pattern on Jacob’s hands grew icy crystals.

‘Enough of the boasting!’ Jacob shouted up at the spirit. ‘You will do none of those things. You will serve me until I grow tired of you, or I will take you to one of the prisons where they store your kind like bottled wine.’

The Djinn brushed the filthy hair from his forehead. Each strand was made of flexible glass and was worth a fortune anywhere behind the mirror.

‘That was not very respectful!’ he whispered. His face was scarred, and the left ear was torn off. In their cold homeland, Djinns were often used in wars.

‘Good. What are my master’s wishes?’ he purred. ‘The usual? Gold? Power? Your enemies laid out at your feet like swatted flies?’

The bottle was so cold that Jacob’s hands were getting numb. Hold on to it, Jacob!

‘Give it to me!’ The Djinn leant down so far that his glass hair brushed against Jacob’s shoulder. ‘Give me the bottle and I will get you whatever you desire. If you try to keep it, I shall wait day and night for my chance to kill you. I have seen nothing but brown glass for a long time, and your screams would help drive out the silence that still numbs my ears.’ The idea brought a smile of pure delight to his sly face. Djinns liked to talk nearly as much as they liked to kill.

‘You can have the bottle!’ Jacob called out. The stench of sulphur emanating from the Djinn’s grey skin was so strong that he nearly threw up. ‘For one drop of your blood.’

The spirit bared his teeth, which were as grey as the rest of his body. ‘My blood?’ His grin was pure malice. ‘What’s killing you? Poison? A disease? Or is it a curse?’

‘What is it to you?’ Jacob replied. ‘Do we have a deal or not?’

The grin turned murderous. His kind of Djinn usually tried to bite off the head of whoever handed him his bottle. Jacob knew of two treasure hunters who’d died that way. Djinns had strong teeth. You’d better be quick, Jacob. Very quick.

The spirit offered his hand. ‘We have a deal.’ His little finger alone was longer than a human arm.

Jacob closed his fingers more firmly around the bottle, though the glass was scorching his skin. ‘Oh no. Your blood first.’

The spirit bared his teeth and leant over Jacob with a sneer. ‘Why don’t you come and get it?’

Exactly what Jacob had been waiting for.

He grabbed hold of one of the glass hairs and pulled himself up. The spirit snatched at him, but before the Djinn could reach him, Jacob had already rammed the bottle up his nose. The spirit howled and tried to pull it out with his massive fingers. Now, Jacob! He jumped on to the Djinn’s shoulder and sliced the tattered earlobe with his knife. Black blood spurted out. Jacob rubbed it on his skin while the spirit still tried in vain to pull the bottle from his nostril. His grunts and groans sent ice crystals dancing through the air. Jacob jumped off the Djinn’s shoulder. He nearly broke his legs landing on the icy flagstones. On your feet, Jacob! The chapel’s roof burst under the pressure of the spirit’s barbed back. Jacob slithered towards the door.

Go, Jacob!

He ran towards the tall pines behind the chapel, but before he could reach the protection of their branches, he was grabbed by icy fingers and lifted up into the air. Jacob felt one of his ribs break. Dangerous medicine.