IF JACK HAD been right in front of her, Nim would have called out. She might have even if it had been Leonora. But Tiffany was the last in the line before her, so Nim didn’t say anything. What if she was wrong, and this was only a hole in the rock, not a real cave? She had to know what it was before she could share it.

There wasn’t time for that now.

She rushed to catch up. The visitors were so nervous of falling off the narrow cliff path that they hadn’t even noticed she’d dropped behind.

‘This is what we’ve come to see!’ Jack announced, at the entrance to the Emergency Cave. Everyone followed him in except Tiffany. She stayed outside with her back pressed to the cliff wall, staring anxiously down at the sea.

She’s acting like there’s something to be scared of in the cave! Nim thought indignantly.

The Emergency Cave used to be where they bunkered down during house-wrecking storms, but now it doubled as Jack’s how-do-algae-grow-in-the-cold laboratory. He still did experiments in his lab behind the house, but to find algae that could be a fuel, he needed to know how fast they could grow when they were cold. So as well as ropes, torches, and cans of emergency food like rice pudding and baked beans, the cave held rows of test tubes and Petri dishes.

‘Fascinating!’ said Leonora, studying a tube full of shimmering algae.

Nim glowed brighter too, knowing that all these scientists had come to see Jack’s research, and that somehow, this meeting might change the world. She stayed happy the whole walk back to the camp, even when Tristan made vomiting noises at the rotten-egg smell from the Hissing Stones and Tiffany stole a yellow flower off a bowerbird’s nest.

THAT NIGHT EVERYONE collected driftwood from the beaches and sticks from the forest to make a giant bonfire on the sand. They roasted sweet potatoes from Nim and Jack’s garden, and toasted marshmallows that Anika had brought from the city.

Nim’s marshmallow caught on fire. She blew it out fast. She’d never had a marshmallow before, and she didn’t want it all burned up before she’d tasted it.

‘That’s my favourite way too,’ said Edmund, poking his stick into the fire till the marshmallow was flaming bright. He blew it out, pulled off the ashy cover, and sucked the melting white mess off his stick.

Nim tried, and he was right. She still liked sweet potatoes better, but flaming marshmallows were more exciting.

After dinner, the adults pulled their fold-out chairs closer around the campfire and talked science talk. Jack told them about the experiments he was doing with algae.

‘We need to find a fuel that doesn’t destroy land or oceans, and doesn’t use up crops that people need for food.

Algae grow fast, and some of them produce oil. But the ones I’ve found that grow fast don’t make oil, and the ones that produce oil don’t grow fast. I’m hoping that with all of us working together, we’ll find the answer to how they can do both.

‘It was a big decision to invite you,’ he continued, ‘because Nim and I have worked very hard to keep our island secret. The ancestors of its plants and animals have lived here for thousands and even millions of years, and we want to make sure that they always stay safe in their own environment. But the island is part of the world, and right now we need to work together for the whole world’s environment to become safer.’

Everyone smiled and clapped, then Lance gave a speech about how honoured they were to come here, and about being part of the world family of scientists, and how he hoped that everyone here respected the island as much as he did. It was quite a long speech, and Nim closed her eyes as she rested her head against Selkie’s warm back. She barely even heard Anika talking about seaweeds and kelp, the biggest algae of all, or Ryan discussing why it was important to know exactly where the ocean’s temperatures were changing most, and what happened to the algae that grew there.

But she woke up when Leonora began to speak, because the elegant biologist made her science into a story. Even little Ollie sat quietly to listen.

‘Algae were the first form of life,’ said Leonora. ‘Learning about their history will give us clues about the algae we have now.’ Then she told them about the fossils she’d found in different places around the world: dinosaur bones and footprints, fern leaves and seashells.

‘Like your necklace?’ asked Tiffany.

The amber scorpion had its head raised and its pincers spread. In the flickering firelight, it looked as if it was still angry and struggling to get out.

‘My lovely little friend, caught in tree sap millions of years ago, but still perfect and fierce,’ said Leonora, stroking the stone.

Tiffany shuddered.

‘It’s not their fault they’re poisonous,’ Leonora said severely. ‘I’m like Nim: I love all creatures, whether they’re ugly or beautiful. That’s why I’m a biologist.’

Nim swelled with pride all over again. She forgot that a second ago she’d been shuddering with Tiffany, because she hated to think of any animal struggling and trapped.

‘You see,’ Leonora continued, ‘even though we’re studying algae now, if we find a fossil on the island, no matter how small, it could still help us on our quest.’

WHEN THE FIRE’S embers died down, Jack and Nim headed up the trail to their house. Fred dozed on Nim’s shoulder. She hugged Selkie goodnight, so that her friend could go down to the rocks where the king of the sea lions was barking for her.

But Selkie hadn’t let Nim out of her sight since the scientists arrived, and she wasn’t going to start now. She galumphed up the hill with them, not caring that the trail was narrow and littered with sticks and rocks.

‘It’s okay,’ Nim told her, ‘they’re not Troppo Tourists!’

HRUMPH! Selkie snorted, so loudly that Alex came out to see what was wrong. Nim knew that meant Alex had finished writing for the day. When Alex was inside a story, a whole herd of sea lions couldn’t get her out of it.

‘Doesn’t Selkie trust your visitors?’ she asked.

‘Two of the kids were rude to her,’ said Nim. ‘But she was happy about seeing Edmund. She even gave him a kiss when she thought I wasn’t looking.’

‘But Selina Ashburn, the biologist who was supposed to bring Edmund, couldn’t come,’ Jack told Alex. ‘She and Peter Hunterstone were taken ill at the last minute, so Lance and Leonora Bijou took their place.’

‘It’s lucky they were the same kind of scientists,’ said Nim.

‘Ah,’ said Alex, with a funny sort of smile.

‘What does Ah mean?’ Nim asked.

Alex laughed. ‘It means I’ve been writing so many stories I forget that there aren’t nearly as many bad guys in real life. And that sometimes amazingly lucky coincidences really do happen.’

She started stacking a sprawl of papers covered with diagrams and notes. ‘Speaking of bad guys: I’m trying to work out how much time my Hero has to escape.’

‘Where does he have to escape from?’ Nim asked.

‘A temple. The Bad Guys have set dynamite to explode it… Did you know that it takes forty-five seconds to burn thirty centimetres of dynamite fuse?’

Nim and Jack hadn’t known. They were used to Alex asking questions like that.

‘So I need to work out how fast my Hero can run, and multiply that by how far away he has to get from the explosion, and that’ll tell me how much time he needs before the temple explodes.’

Even though she knew now that Alex Rover wasn’t the hero of the books, and that everything that happened in them was made up in Alex’s head, Nim still loved listening to the stories. She loved the way Alex talked about the characters as if they were friends, and she especially loved when she could help work things out.

So they talked about the Hero and the Lady Hero he was saving, and the jewel that was inside the temple, and when she went to bed Nim realised she hadn’t told Alex all about the real visitors. She’d wanted to tell her about Leonora’s scorpion trapped in amber, and how Leonora was as smooth and shiny as a jewel herself.

She went to sleep hearing the biologist’s silky voice saying that learning about fossils could save the world. Nim was going to do everything she could to help her find something perfect.

And when she did, everyone would want to be her friend again. Even Tiffany.