Moments later, I noticed that the water was changing. The dark rocks below us were becoming more scattered. Stretches of sand started appearing in between them.

Aaron glanced back at me. I swam harder to catch up to him. "It's getting warmer," I said.

He nodded. "Getting shallower," he said. "This is where the depth numbers started getting lower. We're nearly there."

His words spurred me on, and I kept pace with him as we swam in silence. The water grew warmer still. The dark brooding rays and sharks we'd been pa.s.sing along our way were replaced by brightly colored fish darting along beside us in long rows and pointed formations like line dancers. It was as though they were escorting us. This way, this way. Nearly there. Follow our moves.

And then the water was so shallow I could see the bottom right below me. My tail brushed sand; reeds stroked my stomach as I floated across them. I stuck my head above the surface and looked around. An island!

"We're here!" Aaron breathed as we pulled ourselves on to the sh.o.r.e.

I sat watching our tails slowly flap at the water's edge, then melt away as our legs returned. "You're sure this is the right island?"

"Positive," Aaron said. "Come on, let's see if we can find whatever it is we're meant to be looking for."

I followed him away from the sh.o.r.e, and we started to make our way around the island. It was long and narrow, so I could see the opposite side from where we were. The beach we'd swum up to stretched all the way along one side, from what I could see. Beyond that it was rocky, with a couple of small hills and a few trees dotted here and there. It shouldn't take us long to get around.

Just a shame we didn't know what we were looking for.

Half an hour later, we'd walked all the way from one end of the island to the other, and still had no idea.

Half an hour after that, we'd covered the whole coastline, the rocky hills, every tree - and still had no idea.

"This is hopeless," I said, flopping down to sit on a rock. "There's nothing here."

Aaron searched around, pulling his hair away from his face, looking this way and that. "There must be something," he said. "There has to be." He sat down beside me. "Melody was asking the sh.e.l.l to help her find something. Inside the sh.e.l.l we find a map. The map leads us here. It has to be here."

"I know - I agree, but it isn't here. Whatever *it' is."

Aaron chewed a fingernail. "I just don't get it. What was she trying to find?"

I stared out to sea, seeing nothing but blue ocean stretching out in a huge flat expanse, as it always did. As it had done for years and years.

Years and years . . . ? Of course! "Aaron," I said. "Morvena told us the sirens had been down there for years."

Aaron tilted his head. "Yes? And?"

"So Melody must have had the sh.e.l.l for years. Whatever she's looking for . . ." I let my sentence trail away. I didn't want to say the rest of it out loud.

"It might have gone," he said, finishing it for me.

I nodded. "That makes sense."

We sat in silence for a while, staring out to sea. I picked up handfuls of sand and let the grains trickle through my fingers.

"We'll have to get back there," Aaron said. "Tell Morvena what we found."

"What we didn't find, you mean."

Aaron's forehead crinkled into a frown. "I just don't see what else we can do," he said.

"I know. But if we leave, does that mean we're giving up on Shona? Giving up on any possibility of getting her out of there?"

Aaron took hold of my hand. Wiping the sand from my palm, he stroked it gently. "Of course it doesn't," he said, smiling at me. "We're not giving up on anyone." He stood up, pulling me up with him. "Let's get back there, tell Morvena and Shona everything, and we'll work out a plan together."

And I don't know if it was because we were walking along the beach hand in hand or because Aaron's words had given me a bit of hope, but as we walked, I felt lighter and more positive. He was right. We weren't giving up at all. I'd never give up on Shona. We'd get her out of there!

"Wait!" Aaron said, letting go of my hand. He was looking down and patting his jacket pocket. "Oh no!- But it can't have!" he mumbled. His face had turned white.

"What's up?" I asked.

He looked blankly back at me. "It must have fallen out while we were scrambling on the rocks," he said, glancing rapidly all around us. "How could I have been so careless?"

"What?" I asked.

"The sh.e.l.l," he said, panic cracking the edges of his words. "It's gone."

"What do you mean, the sh.e.l.l's gone?" I asked, staring at Aaron: his outstretched empty hands, his pale face.

"I mean it's disappeared," he said flatly. "I've dropped it somewhere. We've lost it. We'll have to retrace our steps."

"Across the whole island?" The next moment, I heard a noise above us in the rocks. A tiny avalanche of stones ran down the hill.

"What was that?" I asked.

"The wind, I imagine," Aaron said absently.

"Aaron," I said, "there isn't any wind. I'm going to look."

"Wait, I'll come with you."

We climbed the small hill, dodging loose stones, slipping on gravel, and searching for the sh.e.l.l as we climbed. The top was as deserted as the beach.

"Nothing," Aaron said. "I told you it was only the -" He stopped. His mouth open wide, he slowly raised a hand to point across to the other side of the island.

"What?" I asked. "What is it?"

Aaron raised a finger to his lips. "Look," he whispered. "On the beach down there."

I followed the line of his hand. He was pointing to a large palm tree on the beach. It was bent over so that its top was almost touching the ground.

"I can't see any -"

"Behind the tree," Aaron hissed.

And then I saw it. Something moved. A figure. A person. And then the person moved again, and I saw who it was.

"Mr. Beeston!" I gasped.

Without stopping to think, I tore down the hill. "Hey!" I yelled as I ran. "What are you doing here?"

Mr. Beeston heard me and looked up. He stood up just before I reached him, shuffling with something in his pocket. And I bet I knew what it was. The sh.e.l.l!

"What are you doing here?" I asked again. I was breathless and panting, but I didn't care.

Mr. Beeston brought himself up to stand as straight and tall as possible. He pulled at the corners of his jacket, and then he looked me in the eye. "Why should I tell you?" he said. "Why should I tell you anything?" Then he turned away and looked out at the sea. "No one bothers to tell me anything, so why should I be any different?"

He didn't sound like his usual self. I couldn't put my finger on it, but there was something different about him. Something - I don't know - something lost. It was as though he wasn't even seeing me, didn't care that we'd caught him following us, or whatever he was doing. What was he doing? My indignation crept up a notch.

"Did you follow us here?" I asked. Then it hit me. "Did you get here before us? Have you found it?"

Mr. Beeston spun around. "Found what? What are you talking about, child?"

"Found the -" I stopped. Yes, exactly. What was I talking about? "Found the lost thing," I said lamely.

He shook his head and laughed sourly. "You know nothing, child," he said. He started to walk away, toward the sea.

"The sh.e.l.l," I called to his back. "Did you steal it?"

"Steal the sh.e.l.l?" he called over his shoulder. Then he stopped. He whirled around and paced back to me. He stood so close to me, I could see beads of sweat breaking out one by one on his forehead. "Steal the sh.e.l.l?" he repeated. "Don't talk to me about stealing the sh.e.l.l. Don't talk to me about stealing anything!" Then he said something under his breath. I couldn't be sure I'd heard him correctly, but it sounded as though he added, "Or anyone."

And then he marched to the sh.o.r.e. Standing at the water's edge, he turned back toward me. "There's nothing here," he called. He turned back to the sea. Holding his arms out wide, he called again. "Nothing," he repeated, his voice breaking on the word.

Aaron was by my side. "What's going on?" he asked.

"I don't know. Mr. Beeston's acting all weird."

"Do you think he found the lost thing?"

I stared down at Mr. Beeston. "I don't know," I said. "Maybe he knew what we were looking for and found it before we even got here. Maybe he's had it all along. I just don't know."

"What about the sh.e.l.l - has he got that?"

I let out a breath. "I'm fairly sure he has, but I can't prove it. Why would he want it, anyway? I don't understand why he's here, what he's got to do with any of this, why he's acting so strangely. I don't get any of it, Aaron."

"Nor do I, but if he hasn't got the sh.e.l.l, I don't know what else can have happened to it."

I looked down at Mr. Beeston, standing at the water's edge, staring out to sea. "Yeah, but if he has, we're not likely to get it back. He's not in a mood to give anything away."

"Maybe the sh.e.l.l isn't that important anymore," Aaron said hopefully. "I mean, we found the map. It didn't have anything else inside it. Perhaps Melody won't mind so much that it's gone."

I laughed - or at least I tried to. It came out a bit more like the sound of a cat being strangled. "Yeah, right. And perhaps we won't get tied up and tortured and left out for the sharks when we go back and tell her we've lost it," I said. "You never know. We could get lucky."

Aaron reached out and took my hand. My anger and fear melted away when he did that and I met his eyes. "Sorry," I said. "I'm just scared."

"I know. It's OK. We'll figure something out. We'll tell them everything. The important thing is that we get back there and make sure that Shona's all right."

I nodded.

"Once we get to the caves, we'll work out our next move together."

I smiled. "You're right. Come on, let's get going."

Aaron nudged his head back toward Mr. Beeston. "What about him?" he said.

I shook my head. "Forget him," I replied, setting off over the rocks. "He's not even worth thinking about."

We got back to the caves easily - Aaron's sense of direction was almost as good as his photographic memory. Soon, we were both leaning out across the waterfall.

"You ready?" Aaron asked. He reached out for my hand.

"We should go separately," I said. "If we stop the waterfall, we might not be able to get down."

He nodded. "OK. See you inside."

A moment later, I was in the waterfall, shooting downward, spinning around and around. It felt as though it went on forever, but it must only have been seconds. Eventually, the waterfall spat me out at the bottom and I lay on the seafloor, shaken, disheveled, and disoriented. A second later, Aaron plonked down beside me in a similar state.

He pulled himself together first. "Come on," he said, shaking himself and flicking his tail as he set off. "Let's go and find Morvena and Shona."

We swam carefully through the tunnels, dodging from rock to rock and hiding behind thick trails of weeds in case any of the others might be around. The last thing we could afford to have happen now was to get captured again before we'd even found Shona and Morvena. I led the way this time. I was pretty sure I knew where they'd be.

"Around this corner," I whispered over my shoulder.

We swam along the rocky ledge till I saw the entrance to Morvena's room. "This is it," I said. "They'll be in here, I bet."

With one more look behind us, we swam inside. The two of them were sitting together on Morvena's big jelly cushion. Morvena was sitting behind Shona, combing her hair. Shona sat still and straight, a faraway look on her pale face.

"Shona!"

She looked up at me and her face broke out into the widest smile. "Emily!" She jumped up from the cushion and swam over to me. Grabbing my arms, she said, "I'd started to think you weren't coming back!"

"I wouldn't leave you here!" I said.

"I thought something had happened to you. I've been so worried. Morvena has too, and so has -"

"We all have," said a soft voice in the far corner. I hadn't noticed anyone else when we came in. My heart plummeted. The others had found them. We were all doomed.

But the siren swam forward, and I realized she wasn't one of the ones I'd met. For one thing, she didn't have a tight, mean face like theirs. And for another, she spoke so softly, her voice could almost have been mistaken for a swish of seaweed in the current. Her face was soft, her eyes were large and round; she shared the long, silvery hair that the others had, but she had none of their sharpness, and the lines on her face seemed to dance around her eyes.

Aaron swam forward and stopped at my side. "Who are -?" he began. And then he stopped. He must have realized in the same moment that I did.

I swam toward the mermaid in front of us. She was smiling down at us. She wasn't likely to smile at us much longer, not once we told her what we'd done - and what we'd failed to do.

"Are you Melody?" I asked hoa.r.s.ely.

She nodded. "And you must be Emily and Aaron," she said gently. Her voice was so kind, I wanted to cry. I wanted to break down and confess, but at the same time, I wanted to spare her from it. I never wanted her to know that we'd lost her sh.e.l.l. Looking at her now, I could tell it would break her heart. How could we do that?

Before I had the chance to think any more about it, Shona grabbed my arm. "Did you find anything?" she asked eagerly. What could we say? How could we do it? We were about to take away the one thing that was keeping everyone in here going: hope.