A sudden light lanced through it all, washing out the detail and causing Nona to shield her eyes.

‘Thought you might appreciate a lantern,’ Ara said in a shaky voice. She held it up and glanced back at the wall she had come through. ‘Well, that was … unnerving.’ She drew a deep, centring breath and gazed around at the sigil-covered walls in appreciation. ‘These are more complex than in the other rooms. There are sentences written here …’

‘How did you get in?’ Nona demanded as she stood.

‘The same way you did, I expect.’ Ara blinked.

Nona doubted that very much. ‘Tell me, exactly.’

‘Well. I went up and down a few times, and I noticed you had vanished. I found a spot where I thought there might be a door and tried everything I knew to open it. It didn’t seem to work but when I got back down to the portrait room it was different … there was a new picture there that … Well, anyway, I didn’t stop to examine it. I just turned straight round and ran back up the stairs. And all along the stairwell were doorways into scenes from my life, as if I could just step back into them. Passing them by was hard. I mean really hard. And I think if I had hesitated they might have just sucked me through. But I didn’t stop. And halfway up was an archway showing you in front of that box. I stepped through and here I am.’ She smiled. ‘Same for you?’

‘My way was a bit more complicated.’ Nona shrugged. ‘The book’s in here if it’s anywhere.’ She nudged the casket with her foot.

‘And we really want to steal? From Sister Pan?’ Ara asked.

‘None of us wants to. I can’t see another way.’ Nona knelt before the casket again and checked it over. No sigil marks. She brought the lock’s threads back into view, hunting for traps or alarms.

‘Won’t she notice it’s gone?’ Ara asked.

‘What’s she going to say? “Which one of you took the forbidden book I wasn’t allowed to have on pain of banishment?”’ Nona identified the threads that would undo the mechanism’s riddle. Three of them. The key must be a complex piece of ironwork. ‘Besides, how often do you think she looks at it? It might be a year before she notices it’s gone. It might be ten years!’

‘So we steal a book to help us steal a different book, which also might not exist.’ Ara sat down, her eyes taking on that ‘witchy’ look as she joined the hunt for any protective thread-work on the casket.

‘It exists,’ Nona said. ‘Abbess Glass wouldn’t have lied to me.’

‘That woman lied whenever it suited her, Nona. There was nothing personal in it.’ Ara’s fingers twitched as she sorted threads, plucking one, examining it, setting it aside for the next. ‘Besides, she was very ill, she could have been confused. She kept calling me Darla the last time I was allowed to visit her.’

‘Jula knew about the book already. She tried to tell me about it years before,’ Nona said.

‘It still doesn’t make sense to me. Sherzal was going to take the Ark and use four shiphearts to control the moon. She didn’t need a book.’

‘The four ingredients of yellow cake are butter, flour, eggs, and sugar. If I gave you those four necessary things you still couldn’t make a cake that Sister Spoon wouldn’t laugh at.’

‘Neither could you.’ Ara took on the nasal tones of Sister Spoon. Ruli was the better mimic but Spoon was easy to do. ‘Novice Nona, that is an excellent cake, perhaps the best yellow cake I have ever seen …’

‘… if the goal in making such a cake were to produce something suitable for hand-to-hand combat,’ Nona continued, holding her nose. ‘However, if I were to wish to eat a cake rather than bludgeon someone to death with it—’

‘Then I would do better to scrape something together from the convent pigsties,’ Ara finished.

‘Not the point.’ Nona tried to look serious. ‘Sherzal wanted the Ark, the palace, the throne. The rest she was just hoping would sort itself out. The Ark was something she needed to get Adoma as an ally. The shiphearts are the necessary ingredients. What we’re after is the cookbook.’

‘It looks clean to me.’ Ara ran her hands over the casket. ‘Try the lock.’

Nona took hold of the three key threads. She didn’t need her hands but it helped her focus. Any lock is a riddle. The threads made that riddle simple, or at least less difficult, and allowed the answer to become clear through suitable manipulation. It took Nona seven tries. Ara had just opened her mouth, her lips shaping the ‘l’ of ‘let me try’ when the required click sounded.

It wasn’t until she opened the lid and gazed upon the contents that Nona first felt guilty. Seeing the bundled letters, a carefully folded scarf of Hrenamon silk covered with a child’s embroidery, the small figures of a horse and a baby carved from dark pearwood, a dozen other personal effects, Nona knew herself for an intruder of the worst kind, trampling a garden of memories.

‘It must be at the bottom …’ Nona could see no sign of a book.

‘We should go.’ Everything Nona had just felt resonated in Ara’s voice.

‘We have to do this.’

‘It’s nonsense anyway.’ Ara stood up to go. ‘If the moon’s secrets were written down in a book they would have been used at the time it was written. Or at least a hundred years later Emperor Charlc wouldn’t have been forbidding the subject and hiding all the books in a vault! He would have used the secret himself. He wouldn’t have left it to two novices in his grandson’s reign!’

Nona looked up at her friend. She wished they could go. She wished they could just shut the box and walk away. ‘If I swore to you that the Ancestor had told me the true alchemy was written in a book … that all we had to do was follow the recipe and base metals would transmute to gold before us … would we be rich?’

‘Well, yes. We’d take the book and—’

‘Which book?’

‘You just said the secret was written in a book. Wait, doesn’t the Ancestor tell you the title?’

‘Just that it’s in a book on alchemy.’

‘Well, no then, we’d be poor because there are a thousand books and scrolls promising the true alchemy.’

‘And there are a thousand books promising all the secrets of the moon. But Abbess Glass, who forgot more things than you or I will ever know, and Jula, who would rather read the dustiest book than eat, and who is sharper than any Mistress Academia I’ve met, both said that this book was different. Jula said it might have something real to say. Abbess Glass promised that it did.’ Nona reached in with infinite care and began to remove items from the casket, committing their positions to memory. ‘And if Abbess Glass said it, sick or not, that’s good enough for me.’

Ara frowned as she had frowned so often over these past weeks. ‘So, if the book in the forbidden library is really what the abbess said it was, how do we use it? How do we prove it? We don’t have four shiphearts. Nobody does! We don’t have access to the Ark. We don’t have anyone to tell who would believe us, Wheel least of all. It seemed like a bad plan when we were just talking about it. Now that we’re actually doing it …’