It was rather hard to concentrate with Sir Hugo defying the stars every few minutes. He peered up at the misty night, shaking his fist whenever the heavens appeared.

‘I defy thee!’ he keened, fogging the window as he pressed his face to it. ‘I bite my thumb at you!’

He bit his thumb a little too hard, then whimpered.

Cordelia had decided to make the mind-changing hat in the workshop at Hatmaker House, where she would only have to hide it from her family, and not every Maker in the Guildhall. She had not seen Goose or Sam on her way out of the museum. Cordelia felt this was for the best: following the princess’s orders was risky, and the fewer people involved, the better. What her friends did not know, they could not get in trouble for.

However, she had found Sir Hugo in a gutter outside the museum, trying to glimpse his lady-love. When she told him the princess’s plan (mainly to stop him singing a ballad), Sir Hugo had insisted on accompanying her home to Wimpole Street. She had agreed, thinking the actor’s presence would provide a good explanation if anybody started asking questions: she could pretend the hat was a costume for his next play.

Cordelia stared around the Hatmaking Workshop at the vast array of magical ingredients, wondering how on earth she should begin.

‘A mind-changing hat,’ she muttered, frowning.

It had sounded so simple when the princess said it, but it would be tricky to make. Minds were amazing and deep: like caverns or mountains, full of hidden mysteries. Changing a mind would be a delicate and complex procedure. But she definitely could not ask anyone for advice, and there were no books with helpful instructions about how to make this sort of hat. Even her aunt’s handwritten recipes did not yield any clues, because this kind of Making was strictly forbidden. Magic that changed minds or hearts was considered Meddling. It was almost as dangerous as Menacing Magic.

‘But I’m doing a good thing!’ Cordelia told herself. ‘The king should change his mind about marrying his daughter off to a six-year-old prince – he’s being horribly unfair!’

Cordelia tucked her hatpin into her hair, and decided she would have to rely on her Making instincts to create this particular hat. She had wildness in her wits and magic in her fingertips, after all, which always led her in the right direction. She just needed to choose ingredients that would work together in harmony to change the king’s mind without producing any unwanted side effects, such as unstoppable hopping. The hat would also need to be small enough to hide inside the king’s crown, but very powerful.

She began by creating a sort of tiny weathervane, which she fitted into the dome of a miniature tricorn, adding Barter Buttons fixed with criss-cross stitches to the points. Then she hammered a piece of Oscillating Ore into an arrow.

Sir Hugo pranced around the room. ‘Seeing my Georgina is like – like –’ He grasped for a simile drastic enough to describe his feelings. ‘Like staring directly at the sun! I must do it every day, lest I die!’

Cordelia did not think staring directly at the sun sounded good for a person’s health. But she had never been in love, and perhaps such things felt necessary at such times.

As the sun was, at that time of the evening, not available to stare at, Sir Hugo fell back to defying the stars for the seventh time. Cordelia looked up from hammering.

‘Can’t you think of something else to defy?’ she enquired.

Sir Hugo looked around.

‘The moon?’ he suggested. ‘Perhaps the very air that I breathe!’

‘I wouldn’t defy that,’ Cordelia advised. ‘You need that.’

Sir Hugo grew quiet, thinking. Cordelia took the opportunity to fetch some Metamorphose Rose petals from a jar, unfurl a Sympathy Ribbon and cut lengths of Permutating Twine from a reel on the wall. She filched pieces of dawn and twilight from velvet-lined boxes in her great-aunt’s Alchemy Parlour (while Great-aunt Petronella was asleep in her chair) and fixed them opposite each other on the weathervane with the twine. The Oscillating Ore arrow went on the front.

‘I just need one last thing,’ Cordelia mused, scouring the workshop shelves as Sir Hugo, tired of defying things, announced that he would inspire Cordelia’s magic with a sorcery-stirring Shakespearean speech.

He leaped on to the window seat, and began chanting: ‘Double, double –’

Cordelia spun round.

‘What?’ she gasped.

Sir Hugo hunched his back and pulled a frightening face.

‘Double, double, toil and TROUBLE!’ he gurned, pretending to stir an enormous pot.

Cordelia’s mouth fell open.

‘Why did you say that?’ she asked.

Sir Hugo looked slightly miffed at being interrupted mid-monologue.

‘’Tis the famous weird sisters’ chant from Macbeth,’ he explained. ‘They delight in creating all sorts of magical troubles!’

Cordelia barely paid attention as Sir Hugo continued with his monologue.

‘Double, double, toil and trouble!’ she whispered to herself. ‘Double, double … Maybe what I heard at the docks was the Troublemakers’ secret code!’

It made a strange sort of sense. Smugglers must need a signal that was short and easy to recognize. She had heard the whisper – double, double – moments after someone had thrown a crate overboard, to be collected by someone swaddled in a cloak.

That was the night before the Troublemakers struck again – Miss Prim at the park! Cordelia thought. If only I knew the name of that ship the cargo was pushed from, I could investigate the crew and find out who knows what!

‘I’ll ask at the docks,’ she murmured to herself, as she searched for one last ingredient to finish the hat properly. ‘Admiral Ransom might have set out on the high seas but Sam, Goose and I can find the London Troublemaker!’

In a dusty jar on a high shelf, she finally found a Lenity Lodestone.

‘Perfect!’ she cried.

Half of the Lenity Lodestone went on the final prong of the weathervane, secured with the Sympathy Ribbon. The other half, also strung on a length of Sympathy Ribbon, she gave to Sir Hugo. As Sir Hugo strode around the workshop, holding the Lodestone, Cordelia held the tricorn above her head and watched the weathervane spin towards him wherever he went.

‘It’s going to work!’ she whispered, as Sir Hugo pirouetted with glee. ‘You just need to wear your half of the stone when we all go into Parliament to watch the king’s speech.’

‘I shall wear it over my heart,’ Sir Hugo declared.

‘The princess will have to find a way to hide the hat inside the king’s crown. Keep the stone with you, and once I activate the hat with a snatch of dawn chorus, the king’s mind will gravitate towards you with harmony and sympathy. The pieces of dawn and twilight will make him change his mind about you and the betrothal.’

Cordelia allowed herself a moment of self-congratulation: this was a particularly tricky hat she had managed to make, without any help at all.

Her smug moment was cut short when she heard her family clatter into the entrance hall. She quickly swept up all evidence of mind-changing ingredients, placing the jar of rose petals in its original position and reeling in the Permutating Twine. She managed to place the tricorn in a hatbox and then pile peacock feathers around it just as she heard footsteps on the landing.

‘Hello, Dilly!’ called Aunt Ariadne, peering into the workshop. ‘What are you up to in here?’

‘Nothing much!’ Cordelia said breezily, hiding an offcut of Oscillating Ore with her foot. ‘Just working on a hat for Sir Hugo’s new play.’

‘A new play, Sir Hugo?’ Uncle Tiberius stumped into the workshop. ‘What’s it about?’

‘It is called The Odious Brat and the Noble Hero!’ Sir Hugo invented. ‘A tale of a daring knight who rescues his princess from a tiny tyrant, wreaking vengeance on the princeling for his crime.’

Sir Hugo slashed an imaginary sword through the room, leaving a trail of (thankfully imaginary) carnage behind him. Uncle Tiberius chuckled as Sir Hugo bent double, visiting what Cordelia guessed was a violent comeuppance on a small person.

‘Does the knight have any help?’ Cordelia asked pointedly, raising her eyebrows. ‘Or does he manage it all by himself?’

Sir Hugo flashed a diamond smile. ‘He has help from a noble and brilliant lady,’ he admitted, bowing deeply in Cordelia’s direction. ‘Without whom he would be utterly lost.’

He took his leave, the Lodestone necklace tucked safely into his shirt. Sauntering off down the street, the actor was twinkled upon by stars, at which – for the first time in months – he felt no need to bite his thumb.

Everybody had to speak softly in the kitchen. Cook had found Turbidus seeds in her pots and pans, loafing in her barrel of flour, idling in her rice and skulking among the jam tarts. She had captured twenty-three seeds so far, by variously trapping them with ladles and jelly moulds, clapping them between oven gloves and snapping the kettle lid over them, then tipping them into an old mustard jar in the Menacing Cabinet where they could cause no more mischief. There were still at least a dozen unaccounted for, but aside from the hearthrug tripping people up and the shop bell ringing when nobody was there, the Turbidus seeds had caused very little harm in Hatmaker House.

Cordelia sat down to supper feeling quite relaxed. There were fretful whispers about Master Ambrosius’s arrest, but she knew that, thanks to her agreement with the princess, he would be released in a few days’ time, the king would announce that Making was free for all, and that Princess Georgina was free to marry Sir Hugo. All would be well before Cordelia and her father set off in Little Bear next week.

Even though they had to do it quietly, everyone heartily cursed the Sensible Party and comforted themselves by inventing appalling hats they would like to make for the politicians to wear. A Wobble-Bottom Bicorn was the favourite.

Prospero reported, over pudding, that Admiral Ransom and his new recruits were setting sail on the evening tide that very night, in the Royal Navy’s fastest ship, the Invincible. They were sailing straight for the island of St Freerest. From there, they would search the seas for the exact location of the Troublemakers’ island hideout. Ignatius had looked smart in his new sailor’s suit, Prospero told them, but Mrs Bootmaker had cried all the way to the docks.

Because everybody was downstairs eating supper, nobody noticed a small green seed inching along the workshop table.

Nobody saw it drop into the hatbox in which the Mind-Changing Tricorn had been hidden, and slink under the brim …