We're heading toward something that looks like an island. As we get closer, I realize it's just a collection of rocks and caves. We swim among the rocks.

"Nathiel," the merman calls. Still holding on to me, he yanks me downward. I quickly adjust my snorkel so I can still breathe.

Below us, a rabbit warren of rocks and tunnels and caves spreads out as far as I can see. It's like a city, packed with too many buildings crammed together as closely as possible.

An old guy with a scraggly beard appears from inside a large crevice. Another merman! We come back up to the surface together.

"Another one?" he says.

"Another what?" I burst out. "Have you got Emily?"

The young merman looks at the older one. "Emily?" he says. "Sharks alive, Nathiel - d'you think this is the one?"

The older merman turns to me. "You're Emily's friend?" he asks.

"I -" What has Emily got to do with this?

"You were looking for her!" he shouts, shaking me.

"Yes!" I burst out. "Yes, I'm looking for Emily. Is she here?"

"Kyle, tell the boss right away," the old merman orders. "Take her to the Lantern Cave first. It's the only safe place above water."

Kyle turns to swim away with me.

"No!"

They both swivel their heads to stare at me.

"Please," I say. A tear streaks down my cheek. I don't care. Anyone would cry in these circ.u.mstances. Anyway, I'm not crying. It's the sun. It's shining right into my eyes. "Please let me go home."

"Where's home?" Kyle asks.

Good question. Home. You know, the place that's about to get pulled down, where I live with two people who can't stand the sight of each other.

"I need to get back to my parents. Please." I blub like a baby. Have I really been reduced to this? Begging to be with my parents!

Nathiel says, "And where are they?"

"I don't know."

He turns to Kyle. "Just get her to the Lantern Cave for now. We can always -"

"They're on a ship," I say.

Nathiel snaps back to face me. "What?"

"They're on a ship, over there somewhere." I point back in the direction I think I came from. I sob. I can't help it. "Please let me get back to it."

The pair of them look at each other.

"A ship." Kyle's eyes are shining. "This is it! First the kraken, now a ship for it. We can get back to work, back to the old days. We need to move fast."

What's he talking about? "Are you going to let me go?" I ask.

Nathiel turns to me, grips my shoulders. "You want to go back to your ship?" he asks.

I nod.

"And you can show us where it is?"

"I - I think so."

Nathiel lets me go. "Handed to us on a plaice," he says, smiling at Kyle. "Good work. We're going to be rich."

Kyle's cheeks flush. He doesn't speak again, just takes me toward a cave. I squeeze through the tiny entrance. It opens out when we get inside. It's dark, and creepy. I can just about make out strange shapes hanging down from the roof. Tiny c.h.i.n.ks of light coming through holes way above me, huge boulders with brown gooey stuff that looks like caramel icing dribbled over them.

He closes a barred metal door and locks it from the outside. I grab the bars. "Wait!"

"We'll take care of you," he says, his face cold and expressionless. "Don't worry."

Don't worry, I say to myself as he swims away from me. I climb out of the water onto a rocky ledge, my body shaking and cold. Sure. Absolutely. Why would I worry? I mean, I've only been locked in a dark cave by myself, with nothing but weird clumps of rocks hanging from the ceiling like enormous crooked fingers pointing at me.

I turn away from the pointing fingers. I've got to get out of here. I just need a plan. I'll think of something.

I shiver as the darkness closes around me.

I swam around my cell for the hundredth time. "Let me out!" I yelled, scratching my hands down the rocky walls. My voice echoed around me. Finally, I slumped in the corner.

The next thing I knew, the door was rattling. I leaped up as Mr. Beeston came in carrying a net basket filled with sh.e.l.lfish and seaweed. He placed it on a rocky ledge beside me. Water crashed around me as I reached for it, throwing me against the sides.

"See that?" he snarled as I grabbed the ledge to stop myself from being thrown back against the wall. "That's virtually constant now. And it'll keep getting worse, until you've done what you need to do."

I didn't reply.

"Eat your breakfast," he said, nudging a finger at the basket. "You need to be strong."

"I don't have to do what you say." The edges of my eyes stung.

"Really? Well, you won't be interested in our new visitor, then. Kyle tells me he's found someone who might make you feel differently."

"A visitor?"

"A friend."

I quickly rubbed my eyes. "You've got her here? But how did you know -"

"Eat up quickly," he growled in a voice that made my skin itch. "It's time for a reunion."

We swam up toward the surface, Mr. Beeston's hand gripping my wrist so tightly it burned. The water grew lighter and warmer as we made our way along tunnels and out into clear water. He pulled me down under a clump of rocks, scattering a group of striped triggerfish. A metal gate filled a gap between the rocks.

"Up there," he said.

My heart thudded. I was really going to see Shona! But what if she wouldn't speak to me after everything that had happened? She'd probably hate me even more now, for dragging her into it again. I had to explain. "Can I see her on my own?" I asked.

"What for?"

"It's personal."

"Ah, friendship, so sweet," Mr. Beeston snarled, his throat gurgling into a laugh. He gripped my arm, his broken nails scratching my skin. "You can have five minutes," he said. Then he fiddled with a lock, and the gate bounced open. I swam through it, along a narrow crack. "And don't try anything smart," he called through the bars.

"I won't."

I swam all the way up to the surface. I was inside a cave, in a tiny pool. Gray pillars lined the edges, their reflections somber in the greeny blue water. A tiny shaft of sun lit up the stalact.i.tes hanging from the ceiling like frozen strands of spaghetti. Where was she?

I swam between the pillars, where the pool opened out. Slimy brown rocks lay all around. Thick cl.u.s.ters like bunches of candles protruded upward from the water, black, as though they'd been singed.

"Shona?" I called.

And then I saw her. Sitting on one of the rocks, her back to me.

But it wasn't Shona.

Her hair was short and black. She turned around. For a moment, she looked shocked. Then she forced her angular face into a twisted smile.

"Hi there, fish girl," she said. There was a smug look on her face, but I was pretty sure her voice wobbled a little. "Long time no see."

"Mandy!"

"Having fun?" she asked with a smile.

"Having fun? You think being captured and locked in an underwater tunnel is likely to be my idea of fun?"

"Oh, sorry. I didn't realize." Mandy examined her nails.

"Didn't realize what?"

"That they didn't like you as much as me. Should have guessed, though. I mean, people never do, do they?"

"What are you talking about?" I gasped.

"Oh, aren't they looking after you nicely? Haven't they promised to take you home?" She glanced at my face. "Oops. Obviously not. Sorry. I always seem to say really hurtful things, totally by accident! Don't worry. You can't help it if people don't like you, can you?"

"Yeah, right, Mandy. I don't think so," I said, clenching my hands into tight fists.

"Whatever." Mandy picked up a stone and threw it into the water. I watched the ripples grow wider and more faint. Then she stepped back up the rock and twirled around the pillars, prancing around the place as though she owned it.

"Why would they like you?"

She stopped prancing and glared at me, eyes wide open and innocent. "What's not to like?"

"Where do you want me to start?" I spluttered.

Mandy frowned. "Anyway, they're stupid," she said quickly. Then she turned to look at me. "Hey, that's a point. They're stupid and so are you. Isn't that funny? You'd think you'd get along better, having something in common like that. Anyway, I don't care. They're taking me back to the boat soon."

"Your boat? You didn't sink?"

"Not that old washed-out lump of tin." She laughed. "No, our new boat. Oh, did I forget to mention that we got saved by a luxury cruise liner? Funny enough, they want to treat us like royalty, too! A shame, isn't it?"

"A cruise liner?" My voice suddenly shook. "What cruise liner?"

"The one that we should have been on in the first place. The vacation we were destined to have. But not to worry. It's all okay now. They're taking me back later today."

"Taking you back? But why?"

Mandy bit her lip before turning away. "Told you. They like me."

"Mandy, you can't trust these -"

A sound of metal on metal clanked below me. Mr. Beeston appeared. "Five minutes is up."

"Why are you taking her to the ship?" I demanded.

"Think we want to be poor forever?" he asked, adding, "Anyway, we're going together."

"Why? What do you mean about being poor? What aren't you telling me?"

"You know all you need to know," he said. "Let's go."

"That's not her!" I yelled, pointing at Mandy. "She's not my friend!"

Mr. Beeston glanced across at Mandy as she turned around. Seeing her face for the first time, he suddenly faltered. "But that's - but you're -"

"You!" Mandy spluttered, looking up to notice him for the first time too. "Mr. Beeston. From Brightport! Does someone want to tell me what's going -"

Just then, a huge wave rushed into the cave, filling it almost to the ceiling. Mandy lost her footing and slipped into the water beside me. I grabbed her.

"Get your hands off me, fish girl," she spat. "I can look after myself!"

"No, you can't. You don't know what you're involved in!" I shouted.

Mr. Beeston had disappeared under the water. A moment later, he resurfaced, fighting his way back up against the tide. I turned to face him. "I'm not doing anything for you till you tell me exactly what's going on."

"Want to bet?" he replied. Mandy opened her mouth to speak, but a wave washed her words away. She spluttered and swam for the edge of the pool. Mr. Beeston lunged toward me, grabbing my arm. I tried to struggle, but he tightened his grip, his fingers scorching into my flesh as he pulled me back toward the grille at the bottom of the cave.

Mandy was shouting something as Mr. Beeston pushed me out, fighting against the raging water. I couldn't hear her words anymore.

"What are you doing with me?" I cried as a wall of white water rushed toward us, flinging me against a wall. "What's going on? Tell me!"