JACK SAT ON Selkie’s Rock for a long, long time, staring out at the empty sky. He felt as if half his world had gone up with Alex’s plane, and that he’d been left behind.

He reread the letter he’d found on the beach: the letter she’d left behind instead of writing a note herself.

Dear Alex

I’m glad the materials I organised for the supply ship were useful; I hope these things will all be, too. I guess that new cabin must be just about finished by now, and you’ve all got clothes to wear again. It was quite amusing to read about your banana-leaf dress in your first email!

Your apartment and furniture have been sold, as you instructed. I’m enclosing all the paperwork. However, just in case you change your mind about staying on that little island for ever, I’m also enclosing your new passport and credit card to replace the ones you lost.

Now, please find enclosed the reason I’ve been so busy: the first copy of your new book. I am very proud to be the editor of this book: I think it’s wonderful, and we’re going all out to make sure it’ll be your bestseller ever.

Please let me know if there’s anything else I can do.

Yours,

Delia Defoe

‘Why would she …?’ said Jack. But no matter how many times he read the letter, it still didn’t explain why Alex had gone.

‘Could she have changed her mind about selling her apartment?’ he asked the sea. ‘Did she suddenly want to go and be famous? And why couldn’t she tell me?’

But the sea didn’t answer, and it didn’t matter what Jack wondered, because Alex was gone – and soon he’d have to tell Nim, which would be almost worse than knowing it himself.

Jack was certain he knew exactly where Nim was. He’d seen her face when she’d opened that big crate of books: she’d be lying somewhere, her head on Selkie’s back and Fred curled on her stomach, lost in a story, not even realising that everything had changed.

ALEX SAT IN the passenger seat of the seaplane, too frozen with sadness to even be afraid. She looked back at the gold sand of Turtle Beach, the black Sea Lion Rocks, the palm tree Nim always climbed and the shack they’d just built, and she wondered if she was making a terrible mistake.

Then she thought about what Nim had said, and knew she cared too much about her friends to stay if Nim didn’t want her.

FRED JUMPED OFF Nim’s shoulder when they hit the water, but he only stayed under long enough to grab one big mouthful of seaweed before popping out beside her.

Selkie was part of Fred’s life, and Fred wanted her back.

They were both swimming as fast as they could, straight out to sea, but the boat was pulling away faster. Nim’s heart was pounding; it hurt when she breathed and she was swallowing water faster than she could spit it out.

I … huff … can’t … go … huff … fast enough! she thought. She rolled onto her back. Fred kept on gliding under the water just beside her.

When Nim had caught her breath and rolled over again, the cruise ship was getting closer – but the motorboat with Selkie and the seal-nappers had disappeared.

It can’t have gone! Nim thought. It must be on the other side of the ship.

That was when she saw the huge pink-and-purple name on the ship’s bow: THE TROPPO TOURIST.

The company that Nim and Jack hated more than anything in the world.

Nim tried to swim faster, but it didn’t take long before she was gasping and swallowing water again. She rolled to her back again; her arms whirred, her legs kicked … and her head knocked hard against a rubber boat.

Hands grabbed her arms. A man and a woman, with horrified faces and matching pink-and-purple T-shirts, stared down at her.

‘Fred!’ screamed Nim.

Fred scrabbled to her shoulder and they were hauled into an inflatable motorboat like the one that had sealnapped Selkie.

‘You said you’d counted!’ shouted the woman whose T-shirt said I’M KYLIE.

‘I did!’ The man named Kelvin answered. ‘There were fifteen kids in that snorkelling group and we took fifteen back. I think.’

‘If you’d counted,’ Kylie insisted, ‘we wouldn’t be fishing this poor kid out of the water just before the ship is set to sail!’

‘Maybe she’s a castaway from that deserted island. We’ve found Kid Crusoe!’

‘You’re not funny,’ Kylie snapped.

Nim didn’t have enough breath to say her name was Nim Rusoe, not Kid Crusoe.

‘Where were you heading to, kid?’

‘To the boat,’ Nim whispered.

She still couldn’t see the other little boat. All she could see was the cruise ship: its white length stretching for ever in front of her, and its towering decks reaching to the sky.

It was the only place Selkie’s boat could have come from, and the only place it could have gone. If Nim was going to rescue Selkie, she had to get on this ship.

Fred sneezed.

‘What is that?’ Kelvin demanded.

‘I don’t care what it is – throw it back!’

Fred clung tight to Nim and glared his fiercest dragon glare. ‘He’s my friend!’ Nim shouted.

‘If you say so,’ Kelvin grinned. He didn’t look as if he really wanted to touch Fred anyway.

‘She’s delirious.’

‘We’d better let her keep it.’

‘Where’s your snorkel, honey?’

‘I don’t know,’ said Nim.

‘Never mind,’ said Kylie, with a big phoney smile. ‘We won’t tell anyone you lost a valuable snorkel if you don’t tell anyone you nearly missed the boat.’

‘Great idea!’ said Kelvin. ‘Look, kid, we don’t want to get you into trouble. Your parents would be pretty mad if they found out you hadn’t stayed with the other kids the way you were supposed to.’

‘You’d probably be grounded all the way to New York City!’

‘Stuck in your cabin for six whole days – you wouldn’t like that, would you?’

Nim felt as if her head was going to explode. ‘Where’s Selkie?’ she shouted.

‘Who’s Selkie?’

‘We haven’t lost another kid, have we?’

‘She’s a …’ But Nim stopped just before she said ‘sea lion’. She remembered the part in Alex’s book when the Hero tricked the Bad Guys out of kidnapping him because they thought he was crazy.

‘… a mermaid,’ said Nim.

‘She’s had too much sun!’

‘Too long in the water!’

‘Wrap her up – grab that jacket.’

Kelvin dropped a pink-and-purple Troppo jacket over Nim and Fred. He still didn’t seem to want to touch Fred.

Kylie looked at him the way Selkie glared at Fred when he ate Nim’s lunch. ‘Don’t worry, kiddo, I’ll get you settled down before you see your parents; you’ll be fine!’

The boat bumped against the ship. A long plank with rope railings led up from the water to a door halfway along the side. Kelvin grabbed a rope, and Kylie pushed Nim up the ramp and onto the ship.