Shona's mouth tightened into a small line. "You go," she said quickly.

"What?"

"Look, it's obvious what's happened. You and Aaron can get through it. You have the power to do that - but it'll only work for you two."

"Shona's right," Aaron said. "That must be what's happening. It's not strong enough for all three of us."

I looked at both of them. My two best friends. Or my best friend and - well, I still didn't know exactly what Aaron was. And I didn't know why the waterfall would stop only for us. We clearly didn't have as much control over our power as we'd thought. Well, that made sense. Where Neptune's concerned, nothing's ever straightforward or easy. But I couldn't help feeling that we were missing something - there had to be some way it could work, if only we knew how.

One thing I did know, though, was that the three of us were in this together.

"We're not leaving you," I said to Shona.

"You don't have a choice."

"Yes, we have," Aaron said. "Do you think we could just go off and happily escape while you're trapped here?"

"But -"

"But nothing," I said. "Whatever we do, we'll do it together. No one's going anywhere till we've figured out how to get us all out. Deal?"

Aaron and Shona looked at each other and then both turned to me. "Deal," they said in unison.

"Good!" I paused. "Now all we need is a plan."

We sat in silence, each thinking our own thoughts. Mine weren't very helpful, so I decided not to bother saying them out loud. I guessed the others felt the same way.

I watched a lone fish with a spiky back slither along in front of me, pecking at the seabed every few seconds, then moving on. It seemed so purposeful. It knew where it was going and how to get there. Would we ever be able to say that about ourselves again?

A swishing noise outside the well broke into my thoughts. A second later, the seaweed curtain lifted. Someone was coming in!

All three of us jumped up and swam to the farthest wall. As we pressed ourselves against the rock, I prayed that we could somehow become invisible against the dark shadows of the well.

A moment later, a face appeared, and one of the sirens swam inside.

She looked around the well and spotted us immediately. Pulling her hair away from her face and swimming over to us, she smiled. "Found you!" she said.

I peeled myself away from the rocks and swam into the center of the well. "Don't try anything. There are three of us and only one of you," I said, trying to make my voice sound big and brave. Easier said than done when you're scared finless and everyone knows it.

The siren swam closer toward me. Instinctively, I backed away.

"I'm not going to hurt you," she said softly. That was when I recognized her. It was the one who had been kind earlier. Morvena.

Aaron swam over to join me. Puffing his chest out and sticking out his chin, he swished his tail hard to make himself taller. He wasn't going to let himself be thrown by seeing one of these sirens for the first time. Or if he was, he certainly wasn't showing it. "Why should we believe you?" he asked. "Why should we even listen to you?"

Morvena looked Aaron in the eye. "I can't make you listen, and I can't make you believe me, either. But I hope you will do both."

"Why?" Shona asked. She was still huddled against the rocks on the other side of the well.

Morvena swam over to her and Shona flinched. The siren answered softly. "Because I think we can help each other."

"Why would we want to help you?" Aaron asked.

I touched his arm. "Wait - let's hear what she has to say. I think she's different from the rest."

Morvena bowed her head slightly. "Thank you," she said. Then she indicated above us. "I saw what you did up there just now," she said. "I was following you - I wanted to make sure you were safe."

"Why would you care?" Shona asked. She obviously wasn't ready to believe that any of the sirens could have good intentions toward us.

"I know what the others are like," Morvena said. "Some of them, anyway. You're children. You're not the enemy - and I'm not a monster."

"So what did you see?" Aaron asked, his tail flicking nervously.

"I saw you do the impossible," she said, her eyes shining and wide. "I saw you swim into the well." She turned to me. "Why didn't you leave?"

"We couldn't," I said. "Shona couldn't do it. Only Aaron and I can swim through it."

"How did you do it?" Morvena asked.

Before I could reply, Aaron elbowed me. "We're not telling you all our secrets yet," he said. "You need to give us something first. Give us a reason to trust you."

Morvena let out a sigh. It sounded as if it contained a hundred years of sadness and regret.

"We can't get out of here," she said.

"I know - because you had your beautiful voices taken away," Shona said from the corner. She still hadn't moved.

Morvena shook her head. "That isn't the full story," she said. "In fact, I'm certain that the singing doesn't have anything to do with our being trapped here. I had suspected it for a long time, but today confirmed it for me."

"What do you mean?" I asked. "I thought you told Shona all about it earlier."

"We did - or at least the others did. I kept quiet, as I often do if I have nothing helpful to say." She turned again to Shona. Tilting her head, she spoke gently to her. "Your singing was the most beautiful thing these caves have heard for many years. It could probably have rivaled Melody's own voice when she was your age."

Shona's face flushed in an instant. "But the others," she said. "They told me it was terrible. They said my singing was useless!"

"That's because they thought the sound of a beautiful siren song would open our prison and let us out. Then when you sang, nothing happened, and they were angry. But, you see, I wasn't, because I know better than they do."

Aaron swam forward. "What do you know? Why would you know more than they do?" he asked, folding his arms. "And why should we believe you, anyway?"

Morvena drew a breath. "Listen," she said. "I'll make a deal with you. I'll tell you everything I know if you promise to try and help."

Shona and I looked at each other. She gave me a tiny nod. I glanced at Aaron, and he did the same. "OK," I said to Morvena. "We promise."

"Well," Morvena began, "many years ago - so long ago, now, it's like a different lifetime - Melody came to me. I was her best friend. I still am." Morvena paused. "I'm her only friend now."

"Why?" Shona asked. "What about the others?"

"They blame her for everything that's happened here. And in a way they're right. But what's the use of blame? It won't get us out of here. All it will do is make our lives even more unpleasant than they already are."

"You were her best friend . . ." Shona prompted.

"Yes. We told each other everything - or at least I thought we did. Until the day she disappeared."

"She disappeared?" I said. "What happened to her?"

"That I've never known. She was gone almost a year. Then one day, she turned up, completely out of the blue, and in such distress that at first I thought she was dying."

"What happened then?" Aaron asked.

"She said that something bad had happened. Something so bad that she was terrified. She decided that she had no option but to go into hiding, although she was sure it would only be for a while. Then she asked three things of me. One, that I never ask her what she'd done; two, that I never tell the others about the state she was in; and three, that I would never desert her."

"What did you say?" Shona asked, her eyes wide, her tail flicking gently.

"I agreed without hesitation. Like I said, she was my best friend. That's how it works."

I gave Shona a quick look. She smiled at me, and her cheeks colored a little. "I know what you mean," she said.

Morvena reached out to stroke Shona's cheek. "I know you do," she said with a sad smile. We all fell silent. Even the fish seemed to slow down and swim more solemnly.

After a moment, Aaron asked, "So what happened next?"

"I told the others that Melody and I were going away for a bit, and they all wanted to come. None of us had seen Melody for so long; we all wanted to be together. We were all such good friends back then. Always smiling, always singing. Melody didn't want them to come; she didn't really want me to come. She seemed to think she'd be putting us in danger. But she was scared, too, and I insisted on coming with her."

"And the others?" I asked.

"Melody couldn't put them off without seeming rude or ungrateful, so she agreed. Remember, we thought it was only going to be for a matter of days. That was what Melody told me; that was what she believed."

"Did the others know about the bad thing, whatever that was?" Aaron asked.

"Melody tried to hide it, but they knew there was something. For one thing, she didn't sing. She never has since the day she came back. We thought at first that she just didn't want to. It was only later - when the rest of us were stripped of our singing voices - that we realized that was what had happened to her, too."

I was captivated by Morvena's story. "So then did Melody tell them what had happened?" I asked.

"No. They knew not to push it. Melody has always been proud, and loyal. If she was determined not to do something, she would stick to her decision, no matter what. She didn't want them to suffer on her behalf, and she didn't want any of us to see how unhappy she was. I'm the only one who's really seen her distress, and even I have never known what it's about."

"She's never told you?" Shona burst out. "I thought you were her best friend!"

"Being someone's best friend doesn't always mean telling them every tiny thing about yourself, you know. Sometimes it means having enough trust to let them have their secrets and still be there for them."

Shona wrinkled her nose. "I don't know about that," she said. "I can't imagine ever having secrets from Emily."

"Me neither," I said, but my cheeks burned as I said it. Was I keeping a secret from Shona by not telling her about my feelings for Aaron? Or had I just not talked about them because I wasn't even sure of them myself?

"Anyway, so we came to this place," Morvena went on. "It was like a little adventure - almost a holiday. Spirits were quite high for a few days. And then the change happened."

"What change?" asked Aaron.

Morvena nudged her head upward. "The waterfall, for one thing. We thought that was why this was such a good hiding place. It was the only way in, but then we realized that it wouldn't let us out."

"How did you hear of this place at all?" asked Shona.

"One of the other sirens told Melody about it." Morvena drew in a sharp breath. "Zalia. I never knew how she found out we were looking for a hiding place. That's another thing Melody has never shared. And I suppose I'll never know if she knew what was going to happen. If she had anything to do with it. My own theory is that Zalia was a traitor from the start - and she was the one who somehow helped to lock us up here."

Shona was staring wide-eyed at Morvena. "And you've been here ever since?"

"So long I only know it's more years than I have wrinkles," Morvena replied with an attempt at a laugh. "After we realized we were locked in, things began to change pretty rapidly. Then we all noticed our voices sounded harsher, and soon we discovered that we could no longer sing."

"So you couldn't get out?"

Morvena shook her head. "Like I said, I've never believed anyone's singing could stop the waterfall." She turned to Shona. "And your singing convinced me totally. If that wasn't good enough to still the falls, no singing could be."

Shona's cheeks flushed deep red as Morvena went on. "We figured out that Melody was being punished for something. But none of us imagined it was anything that serious. We all thought our voices would return shortly and we would go home."

"But they didn't return," Shona said.

Morvena shook her head. "One day, early on, the others were starting to panic. Wailing and screaming every day - it was awful. That was when Melody told us a siren song would get us out, and that we just had to stay calm and be patient and wait for our voices to return. It worked - in as much as it calmed the panic."

"And then what happened?" I asked.

Morvena looked at me. "The waiting began," she said. "Over the long years of waiting, the others have held on to this idea more and more firmly. It is as though this is their faith; this is all they believe in; this is their impossible salvation."

"But you don't believe it?" I asked.

"No. One day, I was going over to see Melody in her room. From outside, I could see that she was crying, and I knew she wouldn't want me to see that. So I waited. But instead of turning away, I watched her. She had something in her hands. Something I'd never seen before."

"What was it?" I asked.

"A sh.e.l.l. A conch. White, with gold and silver flecks running in spirals all around it."

"Swishy!" Shona breathed.

"She was holding it in front of her, talking to it. At one point, she even kissed it! At first, I wondered if our imprisonment was making her crazy. But I swam closer. Staying hidden, I listened to her talking to the sh.e.l.l."

"What was she saying?" I asked.

"She was begging it," Morvena said. "It almost broke my heart to hear her. Begging it to help. Pleading with it."

"What do you mean?" Aaron asked. "Pleading with a sh.e.l.l? What was she saying?"

"The same thing, over and over and over. *Please, please, get us out of here. Release the magic and help me find you.' I've heard her do the same on many occasions since then. In fact, I believe she has done the same thing every single day and night since we've been here."

"Does she know you've watched her?" Shona blurted out, clearly as shocked at the idea of spying on your best friend as she was at the idea of keeping secrets from her.

Morvena shook her head, and her long silver hair flickered behind her. "I know her well enough to know she would be devastated to think I'd seen her in such distress." She smiled wryly. "I have my secrets from her, too. To protect her."

This best friend thing was starting to seem more complicated than ever. "So she's protecting you from being upset by not crying in front of you, and you're protecting her from being upset by not telling her you've seen her crying?"

Morvena let out a soft laugh. "That's about the long and short of it, yes."