"So that's pretty much it," I said. Mandy had sat openmouthed through the whole story, hanging on every word like a child listening to her favorite fairy tale. Hearing myself say it all out loud, I thought it did sound a bit like a fairy tale. The only difference was that every word of this fairy tale was true.

"And that's what was inside the sh.e.l.l," she said, pointing to the package Aaron still had folded up in his hand.

Aaron nodded. "We were just about to open it when you came in." He looked up at me. "Ready?"

I nodded.

He unfolded the package, again and again until it was fully open. A plain sheet of paper, covered with hand-drawn squiggles and lines and symbols and strange words that I didn't recognize.

The three of us hunched over it, trying to make sense of it.

"I think it's a map of some sort," Aaron said. "But I don't know of where. It doesn't look like any countries I've seen." He frowned at it. "All those maps back at the castle - I can't think of a single one that looks like this."

"Of course you can't!" Mandy suddenly exclaimed, sitting up straight and staring at us both.

"Why not?"

"Look - the map came from a siren, right?"

"Right," I agreed, trying to ignore the fact that it was drawn on a plain sheet of paper and stuffed inside a sandwich bag. How did a siren get hold of such ordinary things?

"And where do sirens live?" Mandy went on, as though she were talking to a pair of very stupid people. Which was when I realized she was. It didn't matter how Melody had gotten hold of it. The fact was, it was hers - and she was a siren.

"In the sea!" I said.

Mandy folded her arms and grinned. "Exactly!"

"Of course!" Aaron said. "It's a map of the sea!"

He leaned back over the map, pulling it straight and indicating for us to join him. "We had these at the castle, too. It's because it's hand-drawn. I couldn't tell right away," he muttered, clearly embarra.s.sed that Mandy had figured it out before him.

He ran a finger over some lines that looked like contours. "Look. This shows you the different areas and currents of the sea," he went on, taking the lead now that he knew what we were dealing with.

"What are all the numbers?" I asked.

"They tell you how deep the ocean is at that point. And those darker bits there," he said, pointing at some dark gray patches dotted on the map. "They're sandbanks."

"What are those thick arrows?" Mandy asked. They were all over the paper, pointing in different directions, left, right, up, and down.

"They tell you the direction of the tide. Very useful," he replied.

"What about that?" I pointed to a circle in the bottom left-hand corner. It looked like an old-fashioned watch, with a little cross on the top.

"That's a compa.s.s, isn't it?" Mandy said. "The cross on the top is pointing North."

"That's right," Aaron said. He rubbed his chin and stared at the map. "You can tell all sorts of things from a map like this. You can find any point in the sea if you've got the right information."

Which was something we were lacking. We didn't have any information. How were we ever going to make sense of this?

Aaron ran his hand over some roughly drawn shapes dotted on the map - the only bits of it that weren't filled with squiggles and numbers. "These will be our best guide," he said.

"What are they?" I asked.

"Land - islands in the sea. And this one . . ." He pointed at a scraggily drawn oval right in the center of the map. Whoever had drawn it had circled it again and again with a different color. They'd done it so hard, the paper had almost ripped. An arrow pointing toward it made sure it stood out even more. It was different from the other arrows. They were thick and broad. This was more like the kind you draw through a heart to indicate true love.

"What about it?" I asked.

Aaron looked up at me. "This is the place we need to find."

The pieces started falling into place. "Melody wanted the sh.e.l.l to help her find something," I said slowly. "The lost thing, whatever it is, I bet it's out there, on that island. It must be! And if we stand a chance of rescuing Shona from that awful place . . ." My sentence trailed away.

Mandy finished it for me. "We need to find the island," she said. "And we need to find it fast."

Fifteen minutes later, Mandy, Aaron, and I were in the map section of the Brightport library. We had to work quickly. The library closed early on Sundays and we only had an hour to find what we needed. We'd pulled out all the sea maps they had. There weren't many, but we figured they'd probably have the local ones at least. We were banking on the hope that the hand-drawn map would be of somewhere reasonably close. It had to be, or how would Melody have been able to swim there?

Aaron dumped a handful of maps and charts on the table in front of us. "Right," he said. "Let's get started."

I pushed the hood off my head. I'd kept my face hidden in case anyone spotted me on the way over and recognized me from the newspaper. There was hardly anyone in the library, though, and no one was taking any notice of us, so I figured it was probably safe enough to show my face. And anyway, sitting in a library with a hood over my head would probably have attracted more attention, not less.

I opened up a map. It was crisscrossed with lines and numbers, yellow circles, purple blocks. And it was ma.s.sive.

"What are we meant to be doing?" I asked as a feeling of hopelessness washed over me like a wave creeping high up the sh.o.r.e.

"Look for any similar patterns," Aaron said as he placed the sh.e.l.l on the table and propped up our map in front of it. "Same groups of numbers, islands that look similar in shape, or grouped in the same kind of way - anything. We need to find a match." He grabbed a map and started unfolding it. "OK?" he asked.

"OK," Mandy and I replied. Then Mandy opened up a third map and the three of us got to work.

"This is hopeless." Mandy folded up a map and threw it on the floor. The discarded pile was getting bigger and bigger, and the ones we still hadn't looked at were dwindling rapidly. We'd nearly gone through them all. "We're never going to find it."

Mandy was right. We were kidding ourselves. I wasn't ready to admit that out loud yet, though. That would mean giving up on Shona - and I would never be ready to do that. "Come on, we haven't finished yet. We'll find it," I said, trying to inject some optimism that I didn't actually feel into my voice. "We've got to."

I picked up another map and pa.s.sed one to Mandy. Aaron grabbed a third. "Last one," he said.

This was it, then. If we didn't find a match in any of these, we didn't have anywhere else to look. We had to find it.

We studied our maps in silence. Staring in front of me at the hand-drawn map, I scoured the real map, looking for anything that seemed to match.

"Hey, I think I've found something!" Aaron said suddenly. He was pointing at his map, tracing around the patterns on it and glancing up every few seconds at the one from the sh.e.l.l. Mandy and I left our own maps and crowded around him.

"Look - see that combination there?" He pointed to the group of numbers in the middle of the map that showed the depth of the water. "The numbers are the same on this one."

I looked up to compare it with our original map. He was right! And there was something else, too, just a little to the side. "Look - the islands!" I said. "They're not exactly the same, but they're a pretty good match."

"The library map has a lot more of them," Mandy said. "Does that matter?"

Aaron shook his head. "I doubt it. Whoever drew this wasn't trying to reproduce the whole thing." He pointed to the island in the middle of the map, the one with the arrow pointing toward it. "They just needed to draw enough so that someone could find this island."

"So that Melody could find it," I added. We might not know who drew it, or why they drew it, or even why the sirens were really trapped in their underwater prison, but at least a small piece of the jigsaw was falling into place.

"And find what she'd lost," Mandy finished.

Aaron folded up the new map and put it beside the sh.e.l.l and the original map. "And now we can go and find it," he said.

"Whatever it is," I said. I still wasn't sure how we were going to find Melody's lost thing when we didn't even know what it was we were looking for. I had to hope that we'd know it when we saw it - if it was still there.

Aaron handed me the map. "Hold on to this," he said. "I'll put the others back."

"Hang on," Mandy said, reaching into her pocket and looking in her purse. She rifled through it and pulled out a card. "Got it!" she said, smiling. "My library card."

Mandy pa.s.sed me the card and went over to help Aaron put the other maps away.

"Don't forget to bring the sh.e.l.l," I said. Then I turned around - and walked straight into someone. "Ooh, sorry, I -" I stopped.

Mr. Beeston.

"What are you doing here?" I burst out.

"Whatever do you mean?" he bl.u.s.tered. "I've every right to come to my local library, I should think." He scanned the three of us slowly with his beady eyes. "I might ask you the same thing," he added.

"And I might give you the same answer," I said, folding my arms.

"Touche, child, touche," he said with a little laugh. I relaxed a bit. Mr. Beeston didn't scare me anymore.

"Look, we're just helping Mandy with some homework," I said. He might not be a threat to us, but that didn't mean I was going to start telling him what we were really doing here.

"Of course, of course, you carry on now," he said lightly. He waved a hand to let me pa.s.s him. But as I did, he grabbed my arm. "What's that?" he hissed.

I followed his eyes. He was looking at the table. More specifically, he was looking at the sh.e.l.l lying on it. His face had turned as white as the sh.e.l.l.

"It's - we're - I -"

"We found it on the beach," Aaron said quickly, looking up at Mr. Beeston with what was probably meant to be a casual smile. "Pretty, isn't it?" he added.

Mr. Beeston took a couple of steps toward him. He reached out toward the sh.e.l.l. His hand was shaking. "Isn't it just," he said. "Mind if I have a look?" he added in a voice that had as much forced casualness about it as Aaron's smile.

Aaron glanced at me. I shrugged. We couldn't exactly say no, could we? Mr. Beeston didn't know anything about what we were doing, or how significant the sh.e.l.l was. Where was the harm in letting him see it?

"Sure." Aaron held the sh.e.l.l out.

All three of us held our breath as we watched Mr. Beeston study the sh.e.l.l. He turned it over and over in his hands, holding it close to his eyes with the concentration of a watchmaker examining the workings of a particularly complex mechanism.

Aaron broke the silence. "I - er, I think we need to get going now," he said. He held his hand out for the sh.e.l.l.

Mr. Beeston looked up. "What? Oh, yes, of course," he said. He held out a reluctant hand to pa.s.s the sh.e.l.l back to Aaron. "Right you are," he said to no one in particular. He seemed to have gone into a trance.

"Mr. Beeston, are you OK?" I asked.

He turned back to me, nodding vaguely. "Gosh, don't you worry about me," he said, flapping an arm as if to swat me away. "You be on your way now." But then he froze. He was looking at my arm. Or rather, the map underneath it. Glancing from the map back to the sh.e.l.l in Aaron's hand, he took a step closer toward me. "The maps," he said. "What are they for?"

"They're for my mom," Aaron said quickly.

Mr. Beeston spun around. "I thought you said you were helping Mandy with her homework?"

"They are," Mandy said. "Aaron's mom is going to help me. It's for geography. She knows a lot about the subject we're doing at the moment."

I could feel my face heat up. It was so obvious we were lying. I felt like a criminal - until I remembered something. We hadn't actually done anything wrong. Then I remembered something else. Shona! If we stood any chance of saving her, we had to get to the island, find whatever it was that Melody had lost, and get the sh.e.l.l back to the sirens before she noticed it was missing.

"Come on," I said, heading for the counter and pa.s.sing Mandy's library card over to the librarian along with the map. "We need to get going." I looked at Aaron and added pointedly, "Your mom will be wondering where we've gone."

And with that, the three of us shoved past Mr. Beeston, shuffled out of the library, and ran back to the beach.

"Be careful, OK?" Mandy stood on the sh.o.r.e under the pier, biting her nails and pacing up and down along the water's edge. The beach was almost deserted. Just a few people here and there: an elderly couple arm in arm in the distance, their faces bent close together. Someone else walking in the opposite direction, throwing sticks into the sea for his dog to chase.

"We will be," I replied.

"And come back if you need anything."

I smiled. "We will."

Aaron glanced around one last time and took a step into the water. "We'd better go," he said.

"You sure you've got it all in there?" I asked, tapping my head. He'd spent the last half hour studying the map and committing it to memory.

"Every symbol and every digit," he said. I believed him. I'd never met anyone with a memory like his. All he had to do was look at information, and it was stored in his brain. Maybe that was what happened when you spent the first thirteen years of your life with nothing much to do except study a whole bunch of maps and books.

"And you've got the sh.e.l.l?"

He patted his big jacket pocket in reply. "It'll be safe - don't worry," he said.

I glanced around, too, before joining him at the water's edge. "Come on, then," I said. "Let's go."

Mandy started to walk away. Then she stopped and turned. "Hey," she called.

I looked up. "What?"

"Good luck."

I smiled. "Thanks."

She nodded and walked away. I looked around one last time, then dived into the water and swam away from Brightport.

"Are you sure we're heading the right way?" We'd been swimming close to the surface so we'd see the island when we got there. But we must have been out here for at least an hour, and there was no sign of an island anywhere.

Long, deep swells lifted us up and carried us along as we scanned the horizon.

"We should be nearly there," Aaron said, squinting into the distance. "That way. Come on."

He dived back under the surface, and I followed him.