For a few moments, Alberto didn't know what to do. What had he done wrong? But then he reminded himself that the man currently walking away, taking long strides and swinging his arms as if furious, was their last chance for help from an adult. Whatever he'd just screwed up, he had to fix it, fast.

"Wait!" he called out, running after.

"No," said Granchio.

Luca came up on the other side of the man. "What's wrong?" he asked.

This made Granchio wheel around. "What do you think is wrong?" he demanded. "If you want somebody to help you with something, you don't talk to them like that!"

That was when Alberto realized.

"Wait, wait, wait!" he repeated, stepping in front of Granchio and holding his hands up. "Bruno! You're Bruno?" What was it the man had said before? I spent half my childhood trying to keep your father out of trouble, and all I ever got...

Granchio stopped. "You didn't know that?"

"No, Sir!" said Luca, joining them. "Nobody told us your name. They all just called you Signor Granchio."

"I knew that," Flavia offered, "but I've never heard them say that before."

"Dad told me," Alberto explained, "that we've all got a little voice in our heads telling us things are bad ideas, and when you hear it, you say Silenzio, Bruno ! to make it go away."

"And then Alberto told me ," Luca agreed. "I asked him why Bruno but he didn't know."

Grachio looked from one to the other, and then sighed heavily. "That figures," he said. "Whenever your Dad had a particularly stupid idea, I'd try to talk him out of it, and that was what he'd say – shut up, Bruno ."

"We're sorry," said Luca. "We didn't know. We'll never say it again."

Alberto wasn't sure he wanted to promise that . Silenzio, Bruno had gotten him through quite a lot, and he knew it was helpful to Luca and Giulia as well. They'd have to be careful here in Napoli, but it was probably okay to keep using it in in Portorosso, where people didn't know Bruno was a real person... although now that Alberto knew that, he was pretty sure he was going to think about it ever time he used the phrase for the rest of his life.

For the moment, however, that wasn't important. There was only one important thing.

"Yeah, we're very sorry," Alberto said. "Will you take us to Portici? Please? I don't want Giancarlo to go back to prison. I don't want to forgive him for leaving me, but I don't want that, either. This time it wasn't even his fault! He was trying to avoid them, but they threatened Polly and Nonna Sofia."

"I don't want them getting hurt, either... and yeah," Granchio said. "I don't want to forgive him, either, but I don't want anything horrible to happen to him. All right," he decided. " Andiamo ."

"Hooray!" said Celia, and then realized nobody else was cheering. She put both hands over her mouth. "Sorry," she added quickly.

"Who are you ?" Granchio asked her.

"This is Celia Gennari," Alberto said. "She's half-human, like me."

"Is she coming?" asked Granchio, with a raised eyebrow.

"We don't have anyone to look after her," Luca said.

"And you?" Granchio looked at Flavia.

"I wanna help," she said. "Nobody likes Uncle Giancarlo, but he's nice to me... and nobody likes me , either."

"We underdogs have to look out for each other," said Alberto. Even if he'd lost Silenzio, Bruno , he still had at least good catchphrase.

"I guess we do." Granchio nodded. "This way."

He signed out of work again. Alberto wondered what excuse he gave, but did not ask – he hoped this man wasn't getting in too much trouble for helping them. Then they stopped at the restroom for a wet towel for Flavia, and everybody piled into Granchio's old car for the drive.

Flavia was quite excited about this. "I've never been in a car!" she said as she scrambled in. Then she tried to sit down, only to discover the problem Carlotta had warned Celia about the day Alberto arrived – there was nowhere to put her tail.

"Zia Sofia doesn't like cars," said Celia, wedging herself in between Luca and Alberto. "She gets sick."

Flavia made several attempts to fit herself into the passenger's seat in front, but could not do so comfortably. Sitting on the edge of the seat, the way she had in the deck chairs on the Gennaris' private beach, would not be safe while the vehicle was moving. In the end, she had to lie down on the floor at the other kids' feet. Granchio didn't like this, but there didn't seem to be any other way to bring her along.

"Is your towel gonna stay wet long enough?" he asked.

"It'll have to," Alberto said.

"I'll breathe slowly," Flavia promised.

Granchio shook his head, and started the car.

There was no conversation as they set off. They needed to figure out what they were going to do in Portici, and Alberto wasn't sure yet. Somehow, they had to stop the thieves from stealing the diamonds and save Nonna Sofia and Polly... but how could they do that without help from the police? Alberto had no idea. He kept looking at Luca, who was normally the idea man, but Luca just looked back helplessly.

"Signor Granchio," Celia said suddenly. "Are you a human or a sea monster?"

Luca and Alberto both sucked in a breath. They, too, had been confused about that when they first met him, but they hadn't dared to ask . Even if they'd been sure it was safe to ask him, the question still seemed rude – the sort of question Alberto hadn't wanted to make a bad impression by asking.

Signor Granchio himself, however, just gave a bitter little laugh. "I might as well be a human. I haven't been in any water deeper than a bathtub in... oh, twenty years now. Since I was about Alberto's age."

"Really?" asked Alberto. He'd had no idea it had been that long.

"Why not?" asked Celia.

"It's because he lost his tail," Flavia said from the floor. "Papa Leo and Papa Giorgio told me about it."

"Giancarlo and I were daring each other to swim under ships as they went in and out of the harbour," Granchio explained. "It was his idea. I told him it was stupid and we were gonna get hurt, but he said I should shut up and stop being a coward – and I was young enough that it got to me. But I got too close to the propeller and it sucked me in and then took my tail right off, up near the top where it won't grow back."

The kids all winced in unison as they imagined how much that must have hurt. It would be as bad as losing an arm or leg. "How were you okay?" Luca asked. "If you lose the end that can grow back, it doesn't bleed that much, but..."

"Well... Giancarlo also saved my life," Granchio said. "He reasoned that your tail can't bleed out if you don't have one, so he dragged me out of the water and climbed up onto the deck of the boat. It worked, too, but funny thing – somehow a tail you don't have can still hurt ."

"Phantom tail," said Alberto with a nod.

Granchio went on. "We couldn't get back in the water, though, because it would have started again, so we just stayed there, waiting for the boat to get where it was going. Took a couple of days. Eventually we got hungry and tried to steal something from the galley, and we got caught. Giancarlo ran and jumped back in the sea, but I couldn't do that, so I had to just stay there and get yelled at for stowing away. They put me ashore in Messina."

Messina was not very far away on the maps of Europa that Luca had been looking at in school, but Alberto didn't have much of a concept of those distances. He only knew that it was on an island, a place where humans could only go on ships.

"What did you do?" he asked.

"I was too scared to get back in the water," Granchio said, "so I had to find work. I got a job on another ship and took that back to Napoli, and I stayed with Zia Sofia on Procida for a while. It turned out Giancarlo hadn't told anybody what happened to me – he just said I'd run off. He got in a lot of trouble for lying about it, but at the time I didn't feel like it was enough. Zia Sofia helped me heal up and get over being scared of the water, but of course I'd lost too much of my tail for it to grow back, and I couldn't really swim anymore. So here I am."

That was an awful thought. Alberto spent more time out of the water than most sea monsters – he'd been living on land basically full-time since moving in with Massimo. Luca did likewise while he was at school in Genova, but neither boy would have wanted to be told they could never get in the water again. Giancarlo had once said that no matter how long they spent on land they were still sea creatures at heart. He must have been at least partially right.

"I'm not mad at him over the accident itself anymore," Granchio said. "I was stupid enough to let him goad me into it. That's on me. But I've never been able to forgive him for just leaving me there, at the mercy of strangers."

"Yeah," said Alberto quietly. He sat for a moment without saying anything. "I'm sorry."

"Don't apologize, Alberto," said Granchio. "You're not the one who needs to."

Silence fell once again.

"So," Granchio added, a few minutes later. "What are you gonna do about this heist thing? You already said you can't call the police or the guys who own the place, so you've got to figure out something else. We'd better think fast, because we'll be there in twenty minutes and if we just sit around somebody's going to see us."

"Right," said Alberto. He still had no idea.

He continued to have no idea as they pulled to a stop outside the trattoria next door to the jewellery factory. There didn't seem to be anything much going on there today... Patrizia was at the front door, saying goodbye to a woman with a shopping bag in her hand. If somebody had robbed the place already, there was no sign.

"Are any of these the cars you saw at Zia Sofia's?" asked Granchio.

"I don't know," Alberto said. He didn't really remember what the cars themselves had looked like. He'd been trying to see who was in them.

"All right." Granchio turned off the engine. "Now what?"

Alberto thought about it, and the only conclusion he could come to was that they simply didn't know enough about what was going on. He opened the car door. "Let's take a look."

"We can't," Luca protested, grabbing his arm. "They'll see us. The thieves know who you are, and Patrizia knows us and doesn't want us in there."

He was right – but Alberto had another idea. "They don't know Signor Granchio, though... or Celia! They can go in and look around. If there's anything funny going on, you'll be able to tell. Celia," he said to the little girl. "Signorina Sorrentino said there was something in the newspaper about the tiara for the Queen of Danimarca. You can ask Patrizia about it."

"Okay!" said Celia eagerly.

"I guess we can do that," said Granchio. "Sounds like spying. Might be fun." He climbed out of the ar and lit a cigarette. "You coming, Piccola ?"

"Yes, Signor Granchio!" she said eagerly. She scrambled across Alberto's lap to get out.

"You can call me Zio Bruno ," he told her. "We're looking for a present for my wife, okay? You're helping."

"You have a wife?" asked Luca.

"No, I don't," Granchio replied.

He took Celia's hand, and the two of them crossed the street to the jewellery shop. Alberto and Luca hunched down in the car to wait. Granchio had left one of the windows partially down so they could have fresh air, but it was still very stuffy in the car.

"I think my towel's getting dry," said Flavia.

"I'll wet it," said Luca. He took it, and slipped out of the car on the far side from the jewellery shop. Alberto watched him run around the side of the restaurant and vanish. A few minutes later, he returned with the towel sopping wet, and returned it to Flavia.

"There's a spigot around the back of the building," Luca said. "I used that." He peeked over the top of the car at the jewellery shop, then opened the door and climbed back in. "Have they come out yet?"

"I haven't seen them," said Alberto. What if something had happened? What if they'd been spotted and kicked out? Worse, what if the bad guys were in there, and had abducted them, too? After all the trouble Alberto had gotten in over the petrol, what would Carlotta and Mike say if he'd gotten Celia kidnapped by jewel thieves?

More time went by. The interior of the car got hotter and more stifling, but nobody dared get out. Finally, however, the front door opened and Granchio and Celia came out. Patrizia waved goodbye to them with a cheerful smile on her face – which turned to a disapproving scowl once their backs were turned. Granchio didn't notice this. He and Celia returned to the car, and he got the motor started.

"How'd it go?" asked Luca.

"The woman in pink did not want me there," said Granchio with a chuckle. "I tramped mud all over her lovely marble tiles." He was, of course, still wearing his overalls and shirt from the shipyard, which were very different from the nice suits and dresses the other customers had. Remembering how Patrizia had disapproved of them , Alberto knew she wouldn't have liked that at all. "She showed us everything in the place, I think. Poor Celia had a hard time getting a word in. I had to stop her and say, my niece wants to say something , and then she was very impatient about it."

"So you asked about the tiara? What did she say?" Luca wanted to know.

"She said they had the cameos for the tiara, but they were not for display to the public," Granchio said. "She didn't mention any diamonds and I didn't think we ought to pry. Might look suspicious."

Alberto frowned. That wasn't very helpful, but it also suggested that nothing much had happened yet.

"They probably won't come here during the day," said Luca, watching as another car arrived in the customer parking lot. "They'll want to wait for nighttime when there won't be people around."

"Yeah," Alberto agreed, and thought for a minute. "When Giancarlo was talking to one of the Signori Rossi, the man said something about getting money out of the safe in his office. That'll be where the diamonds are, I bet. It's the safest place in the shop – that's why it's called a cassaforte ." A strong house .

"That's how it works in movies," Luca agreed. "The diamonds are always in the safe."

That was when Alberto lit up. Suddenly, he knew exactly what they would have to do.

"I've got it!" he said. "Listen: they won't be back until dark, so we've got the whole rest of the day. We're going to sneak in, and steal the diamonds before they can do it! Then when Giancarlo and the humans try, there won't be anything there, so they'll have to go home, and we'll give the diamonds back later!"

Signor Granchio was skeptical. "You're just gonna walk in, take them, and walk out? You said the woman in pink didn't like you."

"I don't think Patrizia likes anybody ," Alberto said.

"We got in before by telling them we were there to see Signorina Sorrentino," Luca remembered, "but she's not there now, so if we try that again, they'll send us away."

"We'll go in through the drains," Alberto decided. "That's how I got in to get Giancarlo out of prison. This used to be a villa, so when people lived here there would have been sinks and bathtubs, and there's gotta be water getting in and out." He pointed back towards the trattoria. "The sea is that way. The water will have to drain there. Let's go."

"Right now?" asked Granchio. "If you go in when the building's full of people and just steal something, you'll be the ones going to prison."

"We have to do it now," Alberto said firmly, "before the real thieves arrive."

They turned west and drove back to the seashore, arriving at the Lido Arturo, a little gravelly beach used mainly by tourists. It was a busy place, surrounded by restaurants and souvenir vendors, so they parked on the other side of the train tracks, and the kids climbed out. After scurrying across the tracks, with the boys sticking close to Flavia on either side so the humans wouldn't see her, they climbed over the retaining wall and down to the seashore.

It didn't take long to find the exit of a storm drain. The water coming out smelled stale and probably didn't have much oxygen in it, but hopefully the tunnel would lead them back to the jewellery shop.

A human wouldn't have been able to find their way in the dark, but sea monsters had an innate sense of direction, necessary for navigating featureless open water, and could always find their way back to anywhere they'd been before. Alberto left his shoes next to the opening and headed in. He kept one hand on the slightly slimy brick wall so he'd know if the tunnel turned suddenly, and held Luca's hand with the other. Luca then held on to Flavia, who held on to Celia.

"If we get separated," Alberto whispered to the others, "keep going until you reach the jewellery shop. We can all find that again. We'll meet there, instead of having to look for each other, okay?"

"Okay," whispered Luca. Flavia and Celia chimed in.

The storm drain, like many such constructions throughout Italia, had originally been built as a sewer and drainage system by the Romans, a very long time ago. Luca had, at some point, told Alberto just how long, but the number was so big it was practically meaningless. The drain followed what had once been the course of a stream uphill, skirting the Parco Superiore , about a kilometre inland until they reached the vicinity of the jewellery shop.

Here, Alberto found a vertical shaft up to a manhole, and climbed the ladder to take a look around. He was on the Via del Corallo, which ran from east to west, right beside the shop. They were almost there.

They found the perfect spot a couple of minutes later, when they saw light coming in through a grate overhead and heard the buzzing of power tools. When the boys had visited the workshop earlier, they'd seen the cameo cutters using machines to shape and polish pieces of shell, which involved a stream of water passing over to take the dust away. That was what was now draining through the grate on the workshop floor, to drip down on top of them.

Alberto climbed up and tried to open the grate, hoping to see just where they were in the room and whether anyone would notice them climbing out, but it turned out there was a latch on one side. His fingers wouldn't fit through the bars to open it. He tried transforming back to human, to get rid of the webbing and maybe reach farther, but it still wasn't quite enough.

"No good," he said to the others, dropping back into the water. "We gotta find somewhere else."

A few metres away they found another drain. This one had a much dimmer light at the top, and the shaft leading down from it was much narrower. None of the older kids could fit into it, but Celia could. They lifted her, and she shimmied up. After a few moments, she returned, her dress dripping with heaven only knew what, to deliver a disappointing report.

"It's dark," she said. "I can't see anything, and the top won't open."

"Well, we'll have to..." Alberto began, but then a light suddenly came on. Everybody looked up to see what was happening, only to have filthy mop water come down and hit them in the faces. Celia screeched in surprise, and Alberto clapped a hand over her mouth to shut her up.

"What was that?" a voice asked from above.

"Oh, no," whispered Luca.

The kids stepped back out of the illuminated square cast on the surface of the shallow water in the drain, and saw the silhouettes of two heads appear, as people looked down to see where the sound had come from. Would the ripples on the surface of the water tell them there was somebody down here? Alberto tried to stand very still.

"Is there an animal in there?" one man asked.

"Hello!" the other called out. The catch on the grate creaked as he opened it, and the hinges groaned. "Anybody?"

The kids remained silent and still.

"Maybe a cat or something," one of the men decided. "We'll have to let the bosses know. All they need right now is an infestation." The light went out again, and they heard a door close.

What made Alberto's heart beat faster, however, was what they had not heard. The men had not lowered the grate again, which meant there was now access to the room.

"Celia," he whispered, "climb up again and get in there, and see if you can find a place where you can open one of the other grates and let us in. You'll have to be really quiet and stay low to the floor, so nobody will see you..."

"Oh, I know!" said Luca. "You can find a fire alarm! It'll be a red box with a button, and the words pulsante allarme antincendio on it. Press the button and there'll be a loud noise and everybody will leave the building." In the dim light, Alberto saw him grin. "At school, a kid got in trouble because his friends dared him to press the button and he did, and everybody had to go outside and wait for the Vigili to arrive."

"Perfect!" Alberto grinned. Thank goodness for Luca's great ideas! "Do that, but then hide after. Once everybody's out, go to the workshop and let us in. We'll wait at the bottom there."

"Got it!" said Celia.

She let the older kids lift her again, and squirmed up the drain to climb out into what was evidently a janitor's closet at the top. Alberto shivered a little, remembering how tight it had been climbing into the prison in Barcellona. That had been almost a year ago now, and he'd grown taller... would he still be able to do that? There was another reason, then, why Giancarlo could not be allowed to go back to prison. This time, Alberto might not be able to get him out.

They saw Celia's tail vanish over the edge of the grate, which she then closed behind her. Then water began cascading down, as she turned on a tap to wash herself off.

"Celia!" Alberto hissed. "No! Somebody will hear!"

It was no use, though – she couldn't hear him over the running water, and he couldn't shout because there was the danger that somebody else would have heard as well. Alberto, Luca, and Flavia could only stand there in the dark trying not to get any wetter until she finished. The water stopped, and then the light brightened and dimmed again – she'd slipped out the door.

The older kids then went back to stand under the other grate, the one that led down from the workshop. They heard the grinding of the machines go on, along with a few voices they couldn't quite make out. A great deal of time seemed to pass, and they began to get nervous. What was taking Celia so long?

"Can she reach the button?" Flavia asked.

Alberto hadn't thought of that, and he could tell from the expression on Luca's face that his friend hadn't, either. What were they going to do now?

Then, to everybody's relief, a loud bell started to clang. Conversation ceased in the workshop, and the machines shut down one by one. Voices spoke, in louder tones although they still couldn't make out the words, and footsteps could be heard as the employees headed for the exits. It must have been only moments after the last person left that a silhouette appeared over the grate, and it squeaked open.

Alberto knew they ought to wait a few moments, to be sure everybody had left, but he didn't want to. He started climbing.

At the top, the lights were still on and the alarm still ringing, and water was cascading down from sprinklers in the ceiling. Alberto scrambled out, and dragged Luca and Flavia after him. Celia was standing there with her hands behind her back, tail switching, looking very proud of herself.

"Did you reach it okay?" Flavia asked.

"I had to stand on a bucket," Celia said, "but I did it!"

"Good job!" said Alberto. "We gotta hurry!"

He opened the workshop door and checked up the stairs. Nobody was there. There was a big red fire alarm bell right over the door, which was ringing so loud it was almost painful. Alberto had to cover his ears as he climbed up to the main floor. The noise got worse there, because there was another such bell at the top of the second set of steps that led to the offices.

People had left the upstairs offices in as much of a hurry as they had the workshop. Several of the doors were standing open, but the door to the Rossi brothers' personal office was not one of them. They had locked it before they left. Alberto still had no idea how to pick a lock, so he had no better idea than to just throw himself against the door, like people did in movies.

It didn't work. His weight wasn't enough.

"Here," said Luca, and took Alberto's right hand. Flavia took the left one. Celia grabbed Flavia's other hand, and they counted to three and hurled themselves against the door. This time, the combined force was too much for the lock to bear. It broke with a crash, and they tumbled through onto the area rug inside.

The rug was coral-pink, the colour of the cameos the company sold and the ties the Rossi brothers had been wearing the day Alberto met them. The kids were covered with grime from their trip through the storm drains, and they left all sorts of smears and footprints on the expensive carpet. Alberto decided that didn't matter – water was being sprayed in here, too, and all the furniture was probably damaged beyond repair. The important thing now was to find the safe. They split up to search.

It was Luca who found it. Behind the desks where the brothers worked were a pair of large paintings, reproductions of famous art featuring fanciful sea creatures like tritones and sirene. Luca had the idea of checking behind these. One of them had a bare wall, but the other swung out on hinges, revealing a hidden compartment containing a small safe. The kids wrestled this out, and it landed on the floor with a thump that shook the building.

"How do we open it?" Flavia asked.

"Didn't think about that," said Alberto, and looked at Luca for help. "In movies they use a bomb."

"Or they have a guy with a stetofonendoscopio," Luca said, "although I'm not sure what he uses it for."

The sprinklers suddenly stopped, and the kids looked up. The nozzle on the ceiling was still spinning, but it seemed to have run out of water. Alberto got up and went to the window. The office looked out over the back of the building, where the car park was. People were milling around there, talking in small groups and looking up at the factory, maybe for any evidence of fire. As Alberto watched, a red truck pulled in, with a ladder and hose on the back. The vigili were here, and the sound of sirens meant more were coming.

"We gotta go," he said.

"How do we get out?" Flavia asked. "This won't fit back down the drain."

That was true – the safe was far too big, and if they couldn't open it, they couldn't take the diamonds and leave it behind. Wherever they went, they would have to take the whole thing with them.

"I know!" Luca said. "The water! It had to come from somewhere, right?" He stood up, pointing at the sprinkler. "A lot of buildings have tanks on the roof to hold water for stuff like that. We can hide in there, and the humans won't even look because they couldn't do it!"

Alberto grinned. "You're a genius!"

They dragged the heavy safe up a third flight of steps, then a fourth, to reach the roof. The door here was locked, too, but it was locked from the inside. They shut it behind themselves, and on the roof itself they found a big, squat cylindrical tank, carefully positioned so that it would not be visible from the ground, spoiling the neoclassical facade of the old villa with its utilitarian shape. This had a hatch in the top with a catch on it, but no proper lock.

They dropped the safe in first. It hit the bottom with a splash and a clang, suggesting there was perhaps a few centimetres of water still in the bottom. Flavia climbed in first, then Celia, then Luca and Alberto. Alberto brought the catch down and then closed the hatch door with it already in place, so it would prop things open a little rather than closing to trap them inside.

Then, once again, they waited.

More sirens arrived, and they began to hear people moving around in the building, although they couldn't make out what anyone was doing or saying. Nobody made a sound. After a while, there was a gurgling sound, and the water level in the tank began to rise again. Once it was deep enough, Flavia ducked her head under to wet her gills, and game up gagging.

"Bleah!" she said. "It's all stale!"

"Well, it's just for putting out fires," Luca said. "They don't care if it's nice water."

Alberto couldn't take it anymore. He cracked the hatch open and looked around, but didn't see anybody. The door to the inside was still closed. Alberto climbed out as quietly as he could, and crept to the edge of the roof to look down.

The fire truck was still there, but the firemen themselves were standing or sitting around it smoking cigarettes, which Alberto thought was a strange thing to do for people who were supposed to stop things from burning. There were also lots of police, who were talking to everybody, taking pictures of the building and writing down notes.

"Oh, carp," said Alberto softly.

With such a fuss going on, the thieve were going to hear about it. They would think somebody had ratted on them, and then they were going to hurt Polly and Nonna Sofia... and it was all Alberto's fault. He and Luca were the ones who'd told Polly somebody was going to steal the diamonds, and then she'd told the Signori Rossi. The owners were therefore on the lookout for an intrusion, so they'd known right away this wasn't just a fire drill.

Alberto really was just like his father, wasn't he? Everything he did went wrong.