"What? About the dowsing?"

She shook her head. "The stuff she said about harnessing nature's energy. That's what we need to do."

"*Harnessing nature's energy'?" I said. "You're getting as bad as Millie!"

"Emily, we need to use anything we can think of if we're going to find this ring," Shona said irritably.

Millie had joined us back out on the deck before I had a chance to reply.

"It's the perfect time to do this," Millie said, scattering the Scrabble letters on the deck and bending the wire around into a new shape. "I don't know why I didn't think of it earlier."

"Perfect time?" I asked. "What's perfect about it?" What could she possibly see as being perfect about anything right now?

"Magical time," she said with a wink. "Spring equinox sometime around now."

"The spring equinox?" I asked, remembering what Aaron had said. The tide was at its lowest point of the year. A brief spark of hope flickered a" but went out almost as fast as it came when I remembered what he'd said next. That there would only be one year when the tide was low enough; and that time had probably already pa.s.sed. I hardly dared hope for the remote possibility that it could be this year.

"In fact . . ." Millie was saying as she reached into the little bag she always carried on her shoulder. She pulled out a small book. It was bound in black felt, with pink and blue feathers around the edges and Orphalese Oracle spelled out in fancy letters along the spine. "If I remember right, this year is even more special."

"Even more special?" Shona asked, her voice tight and high. "Why is it even more special?"

"Let me check." Millie looked through her book, licking her thumb and flicking through the pages. "Aha! Yes, that's it." She smiled. "It is extra special! This year the full moon and spring equinox are at exactly the same time. The same day. And, my word! Fancy that! The full moon is at the same time as the moon's peak." She glanced at me and, probably noticing my blank face, went on. "When the moon has risen to its highest point in the sky, it will also be at its fullest. Very rare. And a" well, I never!"

"What?" I asked, my nerves about to crash and splinter.

"The full moon occurs at midnight!"

I swallowed hard. "At midnight?" I asked, my voice quivering like a freshly caught fish. "Are you sure?"

"Absolutely!" Millie snapped. She tapped the cover of her book. "Emily, you'd be wise not to doubt the word of the Orphalese Oracle. Never been wrong yet, in my experience." She tutted loudly and went back to flicking through the book, squinting and mumbling. "Full moon at midnight on the spring equinox," she muttered. "I bet that doesn't happen often."

Happen often? How about once every five hundred years! Aaron was wrong a" the year hadn't come and gone at all! This was it! This year a" the one chance to find the ring!

"Millie, can I see?"

She pa.s.sed me the book. My hands shook so much that the words started to blur. But I saw all I needed to see. She was right! The full moon was at midnight on the spring equinox! My hands shook so much when I read the next part that I nearly dropped the book. The date!

It was tonight.

I handed the Orphalese Oracle back to Millie in silence. I couldn't make any words come out of my throat.

"Very interesting," Millie said, oblivious to the change in mood as she smiled at us both. Then she put the book back in her bag and picked up the coat hanger. "Now, let's see about this dowsing."

"That's odd," Millie said, frowning with concentration as she waved her coat hanger over the Scrabble letters.

"What? Has it told you where we are?" I asked, edging closer to watch over her shoulder.

Millie shook her head. "It keeps moving over to you." She glanced at me. "To your hands. As though it wants to tell us something about the ring. Watch. It's telling me there's a strong connection between the ring and . . . hold on. It's spelling something out."

I watched her waggle the coat hanger over the letters. It didn't look as if it was doing anything except twitching and wiggling in her hands.

"Something about a star," Millie mumbled as the coat hanger moved across the letters.

Shona hitched herself higher on the side of the deck. "Stars? Maybe it's telling us to use the stars to find our way back."

"No, it definitely has to do with the ring. A strong link with the ring and a" hold on. It's not finished," Millie said, following the coat hanger's progress and reading aloud. "Star l-i a""

"Starlight?" I suggested.

"Could be. Wait." We all watched the coat hanger intensely as it moved to the letter n, then g, then s. After that, it stopped twitching and lay still in Millie's hands.

"Starlings!" Millie said eventually, pulling a hankie out from her bag and wiping her forehead as she put the coat hanger down.

"Starlings?" I repeated blankly. "What have starlings got to do with anything?"

Why? Why had I gone and done it again? Believed that Millie's so-called psychic intuition might bear any resemblance to anything that made any sense? Why?

"I don't know, dear." Millie said flatly. "It sometimes takes a few attempts to work properly. Needs warming up, you know. Why don't you run along for now, and we'll try it again later?"

Shona and I slunk away and left her to it.

"So much for dowsing!" I said, dropping into the water beside Shona. My tail flickered halfheartedly to life, as weak and limp as the few shreds of hope I still had. The full moon was tonight. If we didn't find the ring, the curse would be fulfilled. By tomorrow I would no longer be a semi-mer, and I would have lost a parent.

"Come on, Em. The tide's going to be at its lowest point in five hundred years tonight!"

"But what if it's still not low enough?" I said. "Or what if we've got it all wrong somehow? The curse will be complete tonight. Neptune will take the ring. It's all over." I couldn't bear it a" couldn't even think through to the end of the thought. My future was a black hole, and at midnight I would slip into it.

"You have to believe we can do this," Shona said. Her voice was so full of hope, I couldn't help letting her enthusiasm filter across to me. My heart filled like a tight balloon.

"You're right," I said with new determination. "It's the only chance we're going to get, and we can't afford to miss it. We've got to find that ring a" tonight!"

"Be careful," Shona whispered as she waved me off from the porthole. "And good luck."

"You too," I said with a hopeful smile. "See you soon."

"You're sure you don't want me to come with you?"

"I'm sure," I said. We'd agreed I had to go straight back to the castle and tell Aaron the news about tonight. There was no time to lose. Shona was going to stay behind and fend Millie off if she came looking for us. Thankfully, she'd become so absorbed in her dowsing that she wouldn't notice anything for a while. I wouldn't have long, though. The last thing I wanted was for her to worry about me, on top of everything else. Or to keep a closer eye on me and stop me from going out tonight. That was unthinkable! I'd just have to be careful a" and quick.

I swam off in the same direction, listened to the ring in the same way, sneaked into the tunnel, and finally came up in the pool in the castle's cellar. I pulled myself out of the water and sat on the side to get my breath back. Panting and exhausted, I wondered how many more times I'd be able to swim here. My body was getting weaker by the hour. My tail was getting more patchy, my breathing more scratchy. Just one more day. Please let me hold out for one more day.

A noise creaked behind me. I leaped to my feet.

"Emily!" It was Aaron! He was still dressed all in black, and his hair was tied back in a sleek ponytail; his face shone pale and clear in the semidarkness of the cellar. His smile was the brightest thing on him. "I've been hanging around here since you left," he said, softly closing the door behind him. "I was hoping you'd come back."

"I said I would." I smiled back, almost surprised at how pleased I was to see him.

Aaron took a step nearer the pool, and that's when I noticed something. His feet a" they were webbed. Of course they were. He was descended from Aurora, which meant the curse affected him too. Like me, he was stuck between the two worlds, neither fully one thing nor another. More like me at the moment than ever, as he wasn't quite a semi-mer either. The brief silence that fell between us wasn't awkward. It was the silence between two people who know they understand each other without even using words. It was almost like the way I felt with Shona.

He noticed me looking and shyly held out a hand. "Come on, let me help you out of the pool," he said. This time he didn't s.n.a.t.c.h his hand away. He held it out palm up, fingers outstretched. Showing me. His hands were webbed too, his fingers joined at the knuckle by the thinnest waferlike stretches of skin. As I reached up to grab his hand, it was as though we were shaking on a deal. We were the same. Whatever happened from here onward, we would succeed or fail together.

We sat on the side of the pool. Aaron stared as my tail melted away and my legs re-formed.

"I can't even do that properly," he said. "My legs stick together and my toes flap about a bit, but that's all." He looked at me wistfully. "Just as it's been for the rest of my family, every generation."

"Aaron, we can change it," I said. "That's what I've come to tell you. Tonight's the spring equinox. And the full moon a" it's at midnight!"

Aaron's eyes widened. "Tonight? This is the year? How do you know? The secrecy, the magic!"

I told him about Millie and the Orphalese Oracle. I didn't mention the fact that Millie didn't always get it exactly right. She had to be right this time. She had to be.

"I don't believe it," Aaron said again and again. "I don't believe it. Every spring equinox since I've known about it, I've hoped and wished. I've even searched for the ring myself and prayed the other one would somehow turn up."

"I can't believe I ended up here," I said, looking at the ring on my finger and smiling. I could feel its warmth smile back at me. "I know I've had a few lucky breaks in my life, among all the crazy stuff! But surely that's about as much of a coincidence as you can get."

Aaron shook his head. "It's not a coincidence at all," he said. "The ring brought you here."

"Brought me to the castle?"

"The rings were meant to be together. When one is worn by a semi-mer, it wants to find the other one. While buried, the rings have no power. But when they are free, they want to be together. They're meant to be together. Its own heart brought you here."

We fell silent, lost in our own thoughts, and maybe in our own hopes. "Now we just have to find the pearl ring," he said after a while.

"Not just find it. We have to find it and bring the two rings together under the full moon. It'll be too late after that. As soon as the full moon's pa.s.sed, I won't be a semi-mer. I'll lose the ring again."

"And if we fail . . ." Aaron looked away as his voice failed.

"I lose a parent," I said.

"So do I, Emily," he said, his voice hardening.

"Huh?"

Aaron took a breath. "Some years ago, life wasn't too bad here at the castle. Generations before me, it was a busy place. Years of ships wrecked on the rocks meant that occasionally the survivors found their way here. And as I told you, Neptune has always installed sirens and some mermen to keep the castle isolated. So I've always at least had some company. Much to Neptune's disgust, there has always been love here too. There has always been marriage, always been a determination to cross the forbidden boundaries."

"Between land and sea?"

Aaron nodded and went on. "But with every generation, it was the same. Just as I told you this morning, each one held the same fate. Each died young. The curse lived on from generation to generation. And still does, all these generations later."

I didn't know what to say. I reached out to touch Aaron's arm.

He looked at my hand on his arm, then looked up at me. "Father was the son of a ship's captain. He swore he would stop the curse before it affected my mother. No one ever knows exactly which year it will happen a" only that it's always on the day of Aurora's birthday." He paused.

"Go on," I prompted.

"There's not much to say. He tried to find the ring, and he failed. He searched and searched out there, but those rocks aren't kind, Emily."

"What happened?"

"He drowned."

"I'm so sorry," I said quietly.

"It was three months ago," he added, and I suddenly thought that must be why he dressed so strangely, all in black. He was in mourning.

He turned back to face me, his eyes shining. "That's why we've got to stop this, Emily. Even if the chances of succeeding are tiny, we have to try. We have to. This will be the only chance of our lives, and the only way to stop us both from losing another parent."

"Another parent? But a""

"My mother, Emily," he interrupted. "She's dying. It's Aurora's birthday next week. This is it."

That was when I really understood that this wasn't just about me. It was about life and death. Literally. If we didn't find the ring, Aaron's mom was going to die next week, on Aurora's birthday, exactly as her ancestors had. And Aaron would die young too! The thought made something clutch at my chest. "We'll find the ring," I said firmly. "I promise."

Aaron tried to smile, but even though he twitched his mouth up at the corners, his eyes were still the saddest I'd ever seen in my life. "Come on," he said, lowering himself into the water. "I need to show you something I've just discovered. After you left, I went to see Mother, but meeting you got me thinking. I went back to the chapel and dug around a little more. Emily, I found something I'd never noticed before. Come and see it."

I followed him back to the chapel.

"Through here." Aaron guided me to the back of the chapel. At the end of the last row of seats, a few steps led down to a tiny gap just big enough for us both to stand in.

Aaron felt around along the wall. He pushed it firmly and the wall creaked a" and moved! A hidden door!

I followed him into a dark box of a room.

I looked around, blinking as my eyes grew accustomed to the darkness. Sunlight seeped in from the smallest gaps in the walls, just enough to see around the room: a small rectangle with a long wooden bench all the way up one side, an arched door opposite.

"I never knew it was here," Aaron said, motioning for me to follow him. "Look, I'll show you something strange."

I stumbled across the dark room, my legs trembling with fatigue but anxiety spurring me on. I kept remembering Millie dowsing on the boat. What if she started to look for me? We had to be quick! I shivered as I followed Aaron to the far end of the room. Cobwebs filled every corner.

A row of paintings lined the wall, just as they lined the corridors all around the castle. "More pictures," I said.

Except that these were different. These weren't portraits, or pictures of battle scenes, and they weren't in frames either. They were murals, painted on the walls.

"It's all I've got. Pictures, books, and maps from all around the world. That's my life. That's my school, my history, everything. But none like these." He pointed to the first picture.

Now that my eyes had grown accustomed to the darkness, I studied the painting. A deep blue sky, a churning sea, and a bright white moon shining down on the castle.

"Who painted them?" I asked.

"I don't know. I bet it was my great-grandfather, though," said Aaron.

"The one who made the rings in the cabinet?"

He nodded. "He was obsessed with the curse, with trying to end it. The men in my family always are. These pictures seem like a clue of some sort."

"They are," I said, not even knowing why. The ring burned on my finger. It was the ring that knew the truth. "They are a clue," I repeated. "I'm sure of it."

"A secret clue, hidden from sight."