The day of Unquiet Night arrived. It was blisteringly hot, and Dundoodle was smothered by a blanket of sticky air that caused sleepless nights, bad tempers and sweaty, bum-shaped patches on seats. All the windows of Honeystone Hall were open to let the air circulate, sending miniature dust storms and cobweb-paragliding spiders through the hundreds of forgotten, empty rooms.

Archie awoke, exhausted, from a feverish dream about Dragon-fire and jewels (and a badger called Clive) to find a red leaf lying on his bed. Written on its surface, in golden ink, were the words:

The Tree begins to shed its leaves. Tonight it must be renewed or all magic fails!

It was a depressingly unhelpful message from the Fjurge Brownies. A reminder of how desperate things were. He had failed to find the Treeheart. It was the very first time he had been called into action as Guardian, and he hadn’t been up to the responsibility.

Archie checked his clock – it was almost afternoon! Why hadn’t someone woken him? He’d gone to bed very late, after working with the others on his idea in the factory, but he hadn’t meant to sleep in this long. He wasn’t even sure his idea would work, either. Had the factory workers been able to make it successfully? He sprang out of bed and quickly got dressed, picking up Belle’s journal from his bedside table. He’d kept it close ever since they’d found the secret writing on the recipe.

Running downstairs, he grabbed some toast from the kitchen and, followed by Sherbet, went straight to the factory. Billy and Fliss were already there, waiting for him anxiously in Mr Fairbairn’s office.

‘We’d thought you’d be here ages ago,’ hissed Fliss. ‘Archie, it’s Unquiet Night. I hope you’ve got a Treeheart hidden under your T-shirt, or we’re in trouble.’

‘I haven’t,’ Archie growled. He was tired and scared, his temper frayed, but he still managed a smile when Fliss’s dad appeared, carrying a metal bowl of sweets. They were round and looked a little like marbles, with a swirling yellow and orange pattern.

‘One experimental sample of our newest product,’ said Mr Fairbairn, handing Archie the bowl. ‘The very first sweet invented by young Mr McBudge. I have to say, I’m very impressed with your creativity and hard work. What did you say you were calling them?’

‘Fizzfires,’ said Archie. ‘I hope they do Belle McBudge proud.’

Thanking a puzzled Mr Fairbairn for his help, Archie carried the bowl up to the hideout, followed by the others, panting in the heat of the factory. Blossom had been hiding in Fliss’s bag and Fliss was eager to let the dragon out.

‘It’s already hot enough, without having to hide a dragon about your person,’ she said, as the creature flew out of her bag and buzzed about the twisted pipework. ‘Especially one that’s all fidgety because she doesn’t like sharing her transportation.’

‘Sharing with who?’ asked Billy, as Blossom let out a smoky grumble.

‘Cogswallop,’ said Fliss, showing Billy the clockwork dragon from Miss Clabbity’s shop, which was sat at the bottom of her bag. ‘That’s what I named it. Blossom gets a bit jealous.’

‘Completely bonkers,’ muttered the real-life dragon, as she threw a withering look at the toy, from her perch on Sherbet’s head.

‘It’s going to get hotter, I’m afraid,’ said Archie. ‘A quick blast of Dragon-fire on the sweets will finish them off. Then we’ll have a replacement for the Gingerbread Dragon, something that will protect us from the Mirk – but with a twist.’

Blossom obliged, filling the metal bowl with golden flames. It wasn’t enough to melt the sweets, but Archie could sense the magic in the air as the honeystone crystals formed. The Fizzfires were now enchanted.

‘Belle’s Gingerbread Dragons had honeystone in them,’ said Fliss. ‘I still don’t get what makes these different.’

‘They’re smaller, but they have loads more ginger,’ said Archie, ‘so they’re much more powerful. Belle didn’t have a sweet factory nearby and that’s our advantage. I added sherbet so they have plenty of fizz, just like our Sherbet! They’re practically explosive!’

‘It feels like you’re handing out ammunition,’ said Billy apprehensively.

‘We’re going into combat,’ said Archie. ‘We’ll need every weapon we can get hold of. Magical sweets, dragons and battle-dogs included.’

Sherbet whined.

Archie divided the sweets between three small bags with long string handles and handed one each to Fliss and Billy.

‘We’ll take these with us on the boat to the forest,’ he said, hanging the bag around his neck.

‘I hate to be a bore,’ said Fliss, ‘but we’re still missing one rather important jewel-related item. Without it, these sweets are pointless.’

‘I know!’ snapped Archie. ‘Do you think I don’t know? I’m just as frustrated – more so – than you! This is the best I can do right now.’

Fliss turned red and bit her lip.

Archie sighed. ‘I’m sorry,’ he said. ‘I can’t think straight in this heat – let’s get back to the Hall, it’s not so warm in there.’

The long, corridor-like portrait room allowed for the most movement of air, so the children went there to let tempers cool off. Archie slumped on the floor in front of the painting of Belle McBudge. Again, he reminded himself of the last part of the riddle from Belle’s grave:

Look where my mournful gaze alights

One heart broken, one renewed.

‘Billy,’ he said, staring up at the portrait. ‘Have you found any other pictures of Belle?’

‘No. This is the only image that exists, as far as I know.’

‘Do you think there’s a clue to the Treeheart in the picture?’ asked Fliss.

They stood up and studied the painting. Belle’s gaze was a bit mournful, but what was she looking at? She was looking at herself in a mirror, and she wore a jewelled headband entwined with her hair.

‘She’s wearing jewels!’ said Archie. ‘Is one of them the Treeheart?’

‘There’s that scroll about the McBudge jewels, in the library,’ said Billy running off to fetch it. ‘And I can think of some other records that might help us.’ He came back with a stack of parchment and several books, spreading them out on the floor.

Whilst Billy and Fliss divided the books between them, Archie opened Belle’s journal, flicking through its pages, searching for any mention of jewellery. Perhaps she had written where she kept her headband – a hiding place for her treasured possessions? The old-fashioned handwriting was so difficult to understand!

Time passed. More books were found, more dusty old documents brought out, but none were of any use. Fliss even suggested a room-by-room search of the Hall.

‘That would take years!’ said Billy, pacing the room for the hundredth time. ‘It’s practically an expedition. We’ve only got a few hours left!’

‘It’s no good,’ said Archie finally, sinking to the floor. ‘We’re doomed. Magic in Dundoodle is doomed.’ He stared up at the painting. ‘Come on, Belle,’ he pleaded. ‘Please help me. I really want to do this. Please.’