‘They’re coming up the mast!’

Smokestack was the only passenger left to climb aboard.

‘Hurry!’ Cordelia reached out to pull him into the wind-dinghy.

But the old pirate did not take her hand. Instead, he unhooked the mooring rope. ‘I’ll fight these villains off!’ he told her. ‘Go!’

‘Smokestack, NO!’ Never called.

‘I’d do anything for you Troublemakers,’ Smokestack said with a smile, and let go of the rope.

A snarling sailor burst on to the crow’s nest and Smokestack shoved the wind-dinghy, sending the Troublemakers plunging over the dark jungle. Cordelia whipped round to catch a final glimpse of Smokestack, valiantly fighting several sailors on the crow’s nest behind them.

Never jerked the rudder and they bucked, lurching over the topmost branches of a jacaranda.

‘I can’t control it – too many aboard!’ he gasped.

‘Everyone, lean hard to starboard!’ Goose instructed, throwing his weight across the vessel, pulling Shelly and Jim with him.

The sky boat swooped in an arc as the weight shifted, and then – in a soaring miracle like wind beneath wings – they were sailing through the air.

Far below, Cordelia saw the admiral emerge on to the beach, a pearl-white orb clutched in his hands: the Sea Dragon’s egg! Cordelia clapped a hand over her mouth to stop herself from exclaiming in fury.

The Troublemakers slipped silently overhead, watching sailors load their boats with magical plunder from the island: piles of crystal wrenched from the bedrock, wriggling sacks and buckets of shells, nets crammed with insects and birds. Sun Eaters swirled through the sky, obscuring the Troublemakers from sight as they glided towards the towering masts of the Invincible.

Cordelia began to worry that the splash they would make landing in the water would alert the enemy to their location. She saw the admiral’s cabin, the lit windows casting a bar of golden light across the darkening sea. A huge lantern hung from the stern on an iron frame.

‘Steer for that!’ she said, pointing.

‘Hard to port!’ Goose whispered.

Everyone leaned and the boat swerved.

‘I’ve got it!’

Sam stretched across the air and grasped the lantern frame in one hand. Cordelia managed to grab Sam’s ankles just before she slipped overboard, and suddenly the wind-dinghy and the Invincible were linked together, first by two girls, and then by the mooring rope.

Sam jemmied open a window, using a shard of moonbeam like a crowbar, and the Troublemakers piled into the admiral’s private cabin.

It was full of stolen treasures: skulls were mounted on the walls alongside the stuffed heads of tusked creatures and splay-winged birds skewered through their hearts. There were chests overflowing with gold and jewels heaped against the walls.

‘Blimey …’ Sam muttered. ‘He’s been busy.’

Cordelia inspected the wide mahogany desk covered with maps and papers, as Never – last out of the wind-dinghy – unhitched the mooring rope, quietly tore the silk sail free and hopped through the window as the boat fell into the water and sank. He closed the window, leaving no sign that anyone had used it as an unconventional entrance into the Invincible.

‘We’ve gotta find somewhere ta hide!’ Sam whispered, peeking out of the door. ‘Let’s go – coast’s clear!’

But a piece of paper on the desk caught Cordelia’s eye. Beneath the words FOR THE RANSOM WING was a list of very rare magical creatures and plants.

‘The Ransom Wing?’ Cordelia muttered. ‘What’s that?’

One of the items on the list – the head of a monster for plinth – made her frown with faint recognition. But Shelly pulled her arm as the others milled anxiously by the door. There was no time to waste.

Cordelia, Goose, Sam and the Troublemakers slipped out of the admiral’s cabin, crept along a low corridor and came across a ladder leading down. On the level below, they found themselves in a dark passageway striped with heavy cannons. The air was pungent with gunpowder.

Above, they heard the thud of boots, the bark of orders, and curse words being hurled like hand grenades.

Cordelia saw Never’s teeth glint in the moonlight as he grinned.

‘Thorn’s aboard,’ he said.

They quickly found another ladder leading down, down, down into the bowels of the ship. At the bottom, the walls curved in close, and it smelled of pitch dark and rotten water. They were almost at the bilge.

‘There’ll be a storage hold – here!’ Goose hissed triumphantly, pulling open a trapdoor with a creak.

As Cordelia lowered herself gingerly through the dark hatch, Sam pulled a stick of moonlight out of her pocket and threw it down after her. By the cool glow of the moonlight, Cordelia saw a long, low space stretching the length of the ship, crammed with crates and stuffed with sacks. It would make a good hiding place.

So, while the admiral and his men dragged the plunder on to the Invincible, Cordelia, Sam, Goose and six Troublemakers bundled themselves below as illegal cargo.

The stowaways shut the trapdoor, huddled around the bar of moonlight and met each other’s eyes in the pale silver glow.

‘We should rescue Thorn now!’ Annie declared gallantly.

But Cordelia shook her head. ‘They’ll know we’re here if we do that,’ she said. ‘We’ll have to wait and help her in London.’

‘She’s strong,’ said Billy. ‘She’ll give the admiral hell all the way back.’

‘Make yourselves comfortable,’ Goose suggested, being the expert when it came to stowing away. ‘We’ve got a long journey ahead of us.’

The sacks were full of fruits that had been ripped from vines by the sailors, so there was plenty to eat. And they discovered that, with a little clambering about on crates and some quiet rearranging of boxes, each could create a fairly comfortable bed for themselves.

Cordelia allocated everybody an emergency hiding place, making sure there were cracks between the crates to clamber into and sacks to cover themselves with, in case anybody came down to inspect this portion of the cargo. She had just finished conducting the first emergency hiding-place drill when they heard the anchor drag along the coral reef deep beneath them.

The Invincible was setting sail.

Cordelia wondered what was left of the island they were leaving behind. Her heart ached remembering the distressed wails of the birds and the screams of uprooted trees. The island had been devastated. Its great protector, the Sea Dragon – the descendant of the very creature whose bones had created the island – was dead. Thorn was captured and Smokestack had sacrificed himself so they could escape.

Cordelia lay on her own makeshift bunk in the utter dark, hoping she had made the right decision to bring them all aboard this ship.

They were in the belly of the beast now – and the beast was surging towards London. She heard the music of the sea humming through the hull as the Invincible picked up speed, racing out on to the vast plain of the ocean.

Cordelia did not need to open every chest to know that she and the Troublemakers were lying on a small mountain of the admiral’s plunder. He must have sunk dozens of ships after collecting their treasures. And she’d seen the mysterious Ransom Wing list on the admiral’s desk.

Her fingers tingled, but there was a sad throb in them too: these magical things had been torn cruelly from their rightful places.

Cordelia had a sudden memory of a wide white room full of empty plinths, and the curator Mr Smirke’s pride in telling her: An unnamed benefactor will soon fill this new wing of the museum. He’s collecting things from all around the world!

The dark, twisted scream of that evil metal lump – what remained of Witloof’s soul – flashed into her head.

She had to rescue Thorn from that dreadful fate.

Suddenly Sam, who was on lookout beside the trapdoor, hissed, ‘Hide!’

Everyone slipped into their secret hidey-holes. Cordelia slid down the side of her crate, dragging a sack across the gap to hide herself. Was anybody visible – a toe, an elbow, a tuft of hair? She poked her head up to check, before Sam stuffed the moonlight under her hat and dived beneath a sack.

A moment later, the trapdoor latch snapped.

Cordelia saw a wedge of light widen across the ceiling as the trapdoor creaked open. Someone carrying a lantern was coming down. Through a chink between crates, she saw the dark blue of a sailor’s cap.

The sailor dropped into the cargo hold, flashing the lantern around, casting light into the corners.

Cordelia held her breath. Had he heard voices? Had they been seen sneaking aboard? Was he coming to investigate?

To her horror, he took several deliberate steps in her direction. He paused again, as if listening hard.

Cordelia could hear her own heart beating far too loudly.

The sailor took another step – directly towards her. The lantern light cast a treacherous beam into her hiding place, like an accusing finger pointing her out.

She shrunk away from the light. But the sailor was reaching towards her! His hand grasped the sack above her and slowly peeled it aside.

Light blinded her as she was discovered.