Things began, as they often do, innocuously enough.

It was a cool, overcast June day in Portorosso, and Luca and Giulia had gotten home from school only a week earlier. Luca had spent most of his time so far with his family in the water, but was eager to catch up on what had been happening in town as well. He was sitting with his friends on the edge of the sea wall, watching the tide roll in and listening to Alberto tell the definitely true story of how he had saved Massimo from a giant shark, when Signora Marsigliese approached them.

"Ciao!" Giulia greeted her.

"Buongiorno, bambini," the woman replied. "Ah… may I have a word?"

This was not the way people normally began conversations with adolescents, and Luca's first reaction was to wonder if they were in trouble. It didn't seem likely – he and Giulia hadn't had time yet to get into mischief, and if it were just Alberto she wouldn't have wanted to talk to all three of them. Still, he was cautious as he asked, "is something wrong, Madame?"

"No, not exactly," she replied. "I wanted to ask you a favour, on behalf of Rocco. He's convinced there's a monster in his closet."

Giulia scoffed. "There's no such thing as…"

"As what?" Alberto interrupted.

Luca and Giulia both looked at him, and found him grinning.

"No such thing as what?" he repeated. "As monsters?"

Luca snickered.

"Not in little kids' closets, there's not," Giulia said.

"I've tried to tell him that," Signora Marsigliese sighed. "He says he knows it's there because he's seen it, and he insists he wasn't dreaming. He wants me to ask if you boys would stay the night and scare it away." She gave Luca and Alberto an apologetic smile. "He figures since you're monsters too, of a sort, maybe you can at least talk to it. I'm ready to try anything if it'll get him to sleep through the night again."

"I think we can do that," said Luca. It was always fun to sleep over in a new place. They'd been in Signora Marsigliese's grocery shop plenty of times, but their only glimpse of her home was through the front door when Alberto delivered fresh fish. "Right, Alberto?"

"Yeah, sure," Alberto nodded. "We'll yell a bunch in the middle of the night, and tell him we killed it."

"I'd rather not the yelling," Signora Marsigliese observed, "but yes, please. Tell him it's gone, and we'll all sleep better. Thank you."

It was now Giulia's turn to giggle as the woman walked away, and Luca gave her a questioning look.

"What's so funny?" asked Alberto.

"I was just picturing this giant scary monster, like Godzilla, coming out of the closet, and you two trying to look mean and frighten it away," she snickered.

"We can be scary!" Alberto said indignantly. "The first time I transformed in front of you, you were scared to death."

"Only because you surprised me," Giulia scoffed. "If Luca hadn't pretended to freak out, I'd've figured it out in about five seconds. You are the least scary monster I've ever met."

"Who's the scariest, then?" Alberto wanted to know.

Giulia replied without hesitation: "Luca's mom."

Alberto turned to Luca to see what he thought of that.

Luca shrugged. "She can be pretty terrifying. Anyway, there's not gonna be any monster, so we don't need to worry about whether we can scare it." He thought for a moment, then glanced warily at Giulia. "Right?"

"Of course there isn't," she said. "Why would there be a monster in Rocco's closet? What's it doing in there, besides scaring him?"

The boys had no answer for that, and so it seemed settled. That evening, with the permission of their families, Luca and Alberto knocked on Signora Marsigliese's door. She let them in, and called out to her son.

"Rocco!" she said. "They're here!"

Rocco came hurrying down the narrow steps and into the tiny front hall, most of which was taken up by the large ficus plant under the front window. Signora Marsigliese's son was well-known around Portorosso and everybody agreed he was a very strange child, though not in a bad way. He preferred to watch group activities like football games or the Portorosso Cup race, rather than participating, and even in the winter he liked to have gelato to lick. The oddest thing about him, though, was that despite being around eight years old, he never seemed to speak. He must have done so occasionally, since he'd clearly spoken to his mother about his monster, but Luca couldn't remember ever hearing a word from him.

He did not speak now, either. Instead, he took Luca's hand and led the boys up the stairway to his room.

Like all indoor living spaces in town, this was tiny. The doorway looked in from the foot of the bed towards a window above its head, with just barely enough space for a person to walk around. If they were sleeping in here, Luca and Alberto would have to be on the floor on either side of the bed. Next to the door that led to the hallway was the door to the closet. This was closed, and a chair had been wedged under the handle.

"That's where your monster lives, huh?" Alberto asked.

Rocco offered a piece of paper with a drawing he'd done. It showed a rotund, furry creature with black and yellow stripes like a bumblebee. Its head was decked out with crooked horns, red eyes, and a mouthful of sharp teeth. Two arms each ended in three clawed fingers, and it walked on three legs. It did not resemble Godzilla, or anything else Luca could think of, but it still wasn't anything anyone would want to run into in the dark.

"I think we can take him," said Alberto confidently.

"Yeah, you'll be safe with us here," Luca agreed. "We'll just tell it that it'll have to find a different closet to live in."

"And if it doesn't want to, there'll be trouble!" Alberto said firmly.

Rocco smiled.

Signora Marsigliese served pasta for supper – trofie with tocco de funzi – and then laid out blankets and pillows for the boys on the floor. They settled down with their heads towards the closet so they would see the monster before it woke Rocco. Rocco himself filled a bucket and a pitcher with water and placed them within easy reach so Alberto and Luca could transform quickly.

"Sleep tight, boys," Signora Marsigliese said as she turned out the light. "Let me know if you need anything."

Luca wiggled deeper into his sleeping bag and shut his eyes. It was a little strange to think of trying to sleep with a bucket of water right next to his head. He hoped he wouldn't roll into it and knock it over in his sleep – Signora Marsigliese wouldn't appreciate having to clean that up.

"Does this monster usually show up right as you're going to sleep, Rocco?" asked Alberto.

Rocco, peering over the edge of the bed, shook his head.

"When you wake up in the middle of the night, then?" Luca guessed.

Rocco nodded.

"All right. You go to sleep. We'll keep watch."

The younger boy smiled and lay his head down on his pillow. He looked very happy with the arrangement.

Luca hoped it would be a peaceful night. If Rocco had another nightmare he might be angry that Luca and Alberto hadn't been able to stop the monster coming in. Maybe just having somebody there guarding him would be enough to prevent that.

Signora Marsigliese had a large clock in her upstairs hall, and through the thin walls the ticking seemed very loud. This didn't bother Luca, who was used to hearing clocks in the buildings in Genova. The only clocks in Massimo's house, however, were quiet, and Luca could hear Alberto tossing and turning and pulling the pillow over his head in an attempt to muffle it. Then, just when it seemed like Alberto had finally fallen asleep, the clock began to chime midnight.

"Ugh!" groaned Alberto from under his pillow. "Why does she have that thing?"

Luca held a finger to his lips. "Sssh! You're gonna wake Rocco up."

"How can he be asleep with all that noise going on?" Alberto whined.

"He grew up in this house," said Luca. "He probably…"

Luca stopped there as a different sound intruded – a gentle creak of hinges that seemed terribly loud in the quiet house. Alberto heard it, too, and the boys sat there very still for a moment in the dark before turning their heads towards the closet.

It looked the same as it had before.

Luca breathed out. "Probably the house settling," he decided. That was what Giulia's mother always said when their house in Genova made strange noises in the middle of the night.

"Yeah," said Alberto, and started to lie down again.

Then they heard it again, longer this time – creeeeeeeeak – and as they watched, the door opened just a centimetre or so, before it gently bumped against the chair that had been set up to keep it shut. There was a pause, and then it opened a hair further, the legs of the chair making a scraping sound as they were pushed across the floor. Luca's eyes were riveted on it as it inched towards his face. He wondered if it would keep going until it hit him, and whether he'd be able to wiggle back out of the way quietly enough for whatever was in the closet not to notice him. What if it stepped on him?

The chair stopped moving. Luca kept his eyes on it, barely daring to blink – and to his utter horror, a clawed hand reached out of the closet and moved the chair to the side.

At last Luca was able to tear his gaze away and look at Alberto. He found his friend looking back at him with huge eyes. For a moment neither had any idea what to do, but then Alberto seemed to make up his mind. He grabbed the bucket Rocco had left him, and poured the water over his head to transform. Luca did the same, and as the creature stepped into the room, both boys jumped up and did their best monster shrieks.

The three-legged, bumblebee-striped beast that had just emerged from the closet screamed right back. Rocco sat up straight in bed and squealed. For a long moment, everybody just stood there yelling, and then silence fell again.

The closet monster's glowing red eyes were huge, and it had its clawed hands on his furry chest as it panted in terror. Then it seemed to get a handle on itself and demanded, in the voice of an adult woman, "what are you doing in here?"

Neither of the boys had expected that, and neither was capable of a response.

"Are you with that school group?" the creature wanted to know. "You're not supposed to be on the scare floor!" It – she – looked at Rocco, sitting bolt-upright in bed with his blanket clutched under his chin, and held up her hands. "I'm sorry. This is very irregular," she told him. "I'll get these two back where they belong, and hopefully we can resume normal operations tomorrow. Very sorry." She grabbed Luca and Alberto each by a wrist, and dragged them into the closet.

Except it wasn't a closet anymore. Rocco had showed them the inside earlier – it was not very deep, and contained mostly clothes organized by colour and shoes neatly lined up in the bottom, with a few toys and books on the top shelf. Now the creature escorted the boys through that same door into an enormous, dimly-lit room that seemed to stretch away forever on both sides. The door slammed shut behind them, and the being that had closed it hurried forward to see what was going on.

This second creature seemed to consist mostly of a mass of shaggy grey fur, with knobby-kneed legs sticking out the bottom and two eyes on stalks emerging from the top. It was wearing a hard hat, and had short arms, one of which was holding a clipboard.

"Louise!" it exclaimed. "Louise, what happened?"

"These two were hiding in there waiting for me!" the yellow and black creature replied, holding up her arms and almost lifting the two boys off their feet. "Did you see them get in, Curtis?"

One of the moplike thing's eyes looked Alberto over, while the other inspected Luca, and then the mop below them wagged from side to side as if the creature were shaking its head. "I've never seen these kids before in my life."

There was the sound of murmuring from all around them. Alberto and Luca peered into the darkness and found it was full of creatures of every possible description. A big hulking apelike one had shaggy green fur like moss growing all over it. A red one had three eyes and crab claws. A third had multiple tentacles that it was using to hold on to half a dozen mugs of coffee. The boys inched closer together. No matter what Giulia had said earlier, there was no word for these things except monsters, and not the kind of monster that people meant when they said 'land monsters' or 'sea monsters'. These were monsters in the sense of something scary and unnatural, and they were all looking at Luca and Alberto with annoyed or disapproving expressions.

"They must be with that class that was touring the place," sighed the creature called Louise. "I'll find the rest of them while you reset the station – we're gonna have to give that one a few days off, at least."

"Yes, Ma'am," said Curtis. He pulled a lever, and pieces of machinery on either side of Rocco's door disengaged. "I'll file the report!"

Louise gave her prisoners a shake. "You boys hear that? Your antics might have cost us a door! What have you got to say for yourselves?"

"Um," said Alberto. He was rarely speechless, but this situation had done it.

"Sorry, Ma'am," said Luca meekly.

"You'd better be," Louise declared. "Now, let's go find your teacher."

A metal door at the far end of the room rolled open, and Louise half-led, half-dragged the two boys through it and into the hallway beyond. The light was much better here, almost painfully bright in comparison with the bigger room they'd just left, but there was much less to see – just neutral beige walls and a hard, charcoal-grey carpet. More monsters were moving around here, going every which way, carrying objects both recognizable and not. Some of these stopped and stared as Louise and the boys passed by, but most were absorbed in their own tasks.

"I didn't need this today, you know," Louise said conversationally. "I have a performance review coming up. In this business you have to be twice as good as a man to get half the respect, and there's this jerk in management who…"

"Louise?" asked a voice.

Her furry shoulders slumped. "Yes, Steve?"

Alberto and Luca looked back over their shoulders to see what they had to assume was the creature named Steve, which had just stepped out of a washroom. It was teal blue, and shaped roughly like a human except that it had no head – just a roughly spherical torso with eyes, a mouth, and a moustache in the middle of it. It was wearing a striped tie around what might have been either its neck or its waist depending on how one felt about its unorthodox anatomy, and had a trilby hat sitting on its shoulders.

"Are these two yours?" this creature asked, seemingly startled by the idea.

"No," said Louise. "They were causing trouble on the scare floor. I'm taking them back to their tour, and then I have to get back to work, so…"

Steve clucked his tongue. "Oh, that's right! Big performance review coming up."

"Yes, and I want to go into it on a strong week," Louise said firmly. "I'm all about consistency."

Luca felt a familiar tingling sensation in his toes. He was drying off, and his feet were starting to transform. He looked over at Alberto, and sucked in a breath through his teeth as he saw the fins on his friend's head vanishing into curls of sandy-brown hair. Luca started trying to pull his hand free, but Louise tightened her grip, all while still glaring at Steve.

"I have things I need to be doing, too," Steve said, "so why don't we discuss this over dinner? How about Winsor's Chophouse? You look like a girl who enjoys a good steak."

Louise was not tempted. "Will the rest of the board be there?"

"Nope!" Steve smiled at her. "Just the two of us."

Luca could see his vision changing and feel his hair growing in. Four green fingers became five pink ones, and he had to stand up straighter to balance against the disappearance of his tail. Alberto was struggling, trying to free himself from Louise's paw before she could realize that the boys were a very different kind of monster than she was.

"I keep telling you," Steve went on, "if you really want to advance in your career, you need to make connections. You've got to…" he glanced at Luca, probably intending to tell him to stop squirming, but if so the words never came out. His eyes went wide, and he screamed like a frightened child.

This startled Louise so badly she let go of the boys and took a step back, and Luca and Alberto seized the opportunity.

"Bathroom!" Luca grabbed his friend by the shoulders, and they fled into the washroom Steve had come out of.

"She'll follow us!" Alberto protested.

"She can't! It's the men's!" Luca told him.

Safely inside, they leaned on the sinks and panted for air. They hadn't run very far, but both were on the verge of utter panic.

"Where are we?" Luca asked. "How is all this in Rocco's closet?"

"Do I look like I know?" Alberto demanded.

Luca felt sick. If Alberto wasn't even going to pretend he knew the answer, then they were really in trouble.

There was a sound that Luca recognized as the crackle of a public address system, and a woman's voice began making an announcement. "Ladies and gentlemonsters, we need you to evacuate the building in an orderly fashion. Please do not… hey!"

Some scuffling followed, and the next voice they heard was Steve's. "Code black! Code black!" He shouted. "Containment breach! There are human children in the… ow!"

The first voice spoke again. "There is no need to panic," she declared. "Remain calm, go to your designated emergency gathering points, and let the exterminators do their jobs."

"Exterminators?" Luca whispered, terrified.

Both of them had the same thought at the same time: Louise had assumed they belonged here as long as they looked like sea monsters. Hopefully everybody else would, too. They needed water.

Luca turned the sink taps on full blast and began splashing himself. Alberto did the same and stuck his head under the flow. Face, hands, feet… Luca scooped water up in handfuls and poured it down his collar, and then he and Alberto did each other's backs to bring out their tails and dorsal fins.

"We got this," said Alberto. "We got this. We're just two totally normal closet monsters."

"Right." Luca checked his feet and grabbed his tail to make sure it was all there.

They heard the door open.

"I think they went in here," said the voice of Louise. "I heard one of them shout bathroom, and I… oh." She saw them standing there, huddled nervously close to each other, and blinked in confusion.

Behind her, three more figures entered the room. These were a variety of shapes and sizes, including one that was barely thirty centimetres tall and sitting on a larger colleague's shoulder. All were dressed in yellow plastic suits from head to whatever they had for toes, with reflective visors and a breathing apparatus.

"Didn't you boys hear the order to evacuate?" the tiny one demanded in a squeaky voice.

"We were scared. We hid in here, um…" Luca tried to decide whether the creature who'd spoken was a Sir or a Madame, couldn't, and was forced to leave the end of the sentence hanging there with no vocative at all.

"There's an emergency exit just at the end of the hall," the tiny creature told them, shaking what must have been its head. "Somebody take them outside and let's finish searching the area. If this is another false alarm, I swear…"

"Come on, boys," said Louise, gesturing for them to follow her. Her hands were now covered in bandages.

Alberto and Luca didn't like the idea of going with Louise, but staying here was no good, either. They joined her, dripping on the floor as they went.

"Why are you wet?" Louise asked.

"We're sea monsters," Alberto replied.

"It's not good for us to dry off," Luca agreed.

Louise looked skeptical, but she said nothing more and led them out into the car park. Dozens of bizarre creatures were milling around there, talking to each other or smoking cigarettes while waiting for the all clear to go back inside. The one called Steve was sitting on the hood of a car, pouring out his heart to a one-eyed, egg-shaped creature in a floral dress.

"… and then I realized the kids weren't monsters at all! They were human!"

"That must have been terrifying," the egg said.

"It was! They were awful and hairless and pink!" said Steve.

The egg hesitated. She was bubblegum pink in colour herself, with no hair on a head that sloped right into her shoulders without stopping for a neck.

Steve seemed to realize he'd made a mistake. "Horrid things with big goggling eyes and too many fingers," he added.

The egg narrowed her own gigantic eye, and put her seven-fingered hands on her hips.

Louise, meanwhile, was looking around for something, and seemed to spot it when she found a being with two heads sitting on top of long necks that extended from a very round body. This creature, with a powder-blue cardigan on, was counting a crowd of smaller beasts that Luca wanted to think represented kids a little younger than him and Alberto… but really, who could say?

"Excuse me!" Louise called.

One of the heads turned, while the other continued counting. "Yes?"

"I think these are yours." Louise pushed the boys forward.

The head examined them. "Marie," she said.

The other head kept counting.

"Marie!" the first head repeated.

The second one sighed. "Yes, Jeanne?"

"Do we know these boys?"

The Marie head finally turned to look. "Oh… no, I don't think we do."

Luca was really scared now. What were the monsters going to do when they realized the boys didn't belong here?

"What are you talking about?" asked Alberto. "Of course you do. I'm Alberto and this is Luca."

Luca nodded eagerly.

Marie and Jeanne looked at each other doubtfully.

"I know them," said a voice.

This speaker was one of the apparent children. It was a squat little creature with several crab-like legs and a few too many eyes. He was wearing the top half of a sailor suit, with the cap on his head, and holding a large swirling lollipop.

"They're friends of mine," he announced. "My father said they could come."

Marie and Jeanne looked taken aback by this pronouncement, but the boy just licked his lollipop and waited, confident that the teachers would have to do what he said. Apparently, he was right.

"Oh," said Marie. "Well, then."

"I guess that's all right," said Jeanne. "Come along, then."

Louise shooed the boys towards the teacher as if glad to be rid of them – probably an accurate assessment – and Marie-Jeanne herded them into the rest of the group of children. "All right," Jeanne said, "now that we've got everybody and then some, I suppose we'd better head back. I don't think we're getting the rest of our factory tour."

"Are your friends coming with us back to school?" Marie asked the grey crab boy.

"Yes," he replied firmly.

"All right," Marie said, "everybody onto the bus."

The kids formed a line to a bright yellow bus, and climbed up the steps into the vehicle one by one. Luca looked back over his shoulder for Louise, and found her watching as the mop-like creature came running up.

"Louise! There you are!" Curtis exclaimed. "Can you believe this?"

"I'm not sure I can," she replied, and then thought for a moment. "Those two boys I found… do you remember what they looked like?"

"Uh… I couldn't describe them to a sketch artist," Curtis said, "but there was a purple one and a green one. Lots of fins, long tails, scaly skin. Why do you ask?"

Marie-Jeanne put a hand on Luca's shoulder to urge him along. "If you're coming, you have to keep up," said Jeanne.

"Sorry, Madame," Luca replied, and followed Alberto and the crab boy onto the big yellow bus.

The driver was wearing a uniform like a human bus driver might have, but he was green and had a row of spikes down his back like a cartoon dragon. The name Vasquez was embroidered on one of his pockets, and a bottle of water was sitting within reach on the dashboard. As they passed, Alberto snatched the bottle and poured the contents over himself and Luca.

"Hey!" exclaimed Vasquez.

"We're sea monsters," Alberto told him, handing the empty bottle back. "We're not supposed to dry out."

"Hey, now, you ought to ask!" said Marie, as she and Jeanne brought up the rear. "Even if you are Harry's guests, you need to remember your manners!"

"Sorry, Madame," Luca repeated.

"We're Miss Lavigne," Jeanne told him.

Alberto and Luca followed the crab-like boy named Harry to the very back of the bus, and sat down on either side of him there as the vehicle coughed to life. Vasquez pulled out of the parking lot and onto the road. It turned out to be a very rough ride, and Luca quickly began feeling carsick. He tried to look out the window to keep his stomach calm, but Harry grabbed his arm and pulled him and Alberto in for a private conversation.

"Did you see them?" the crab boy whispered excitedly.

"See who?" asked Alberto.

"The humans," said Harry. "That's what the announcement said: there were humans in the factory!"

Alberto and Luca exchanged a worried glance. "We didn't see any," said Luca.

"No humans where we were," Alberto agreed.

"Oh." Harry let go of them and scowled in disappointment. "Wait, so why did you wanna come with us so bad?"

"We just didn't want anybody to realize we weren't where we're supposed to be," Luca explained.

"Where are you supposed to be?" Harry wanted to know.

The boys exchanged another glance, and silently agreed to change the subject. Alberto offered a hand.

"Alberto Scorfano," he said.

"Luca Paguro." Luca did likewise.

Harry shook each of their hands in turn. "Henry Jeroboam Waternoose the Third. My father owns the factory," he added proudly. "We supply all the scream power to Monstropolis and the surrounding countryside as far as the River Panic."

Alberto nodded as if that made sense. "Uh-huh. So… are you scared of humans, Harry?"

"My father says it would be foolish not to be," Harry replied, "but fear is healthy when tempered with reason."

"Right," Alberto said. "Have you ever seen one?"

"I've seen pictures," Harry replied.

Luca realized he knew where Alberto was going with this, and his stomach sank – he knew in his bones it was a terrible idea.

Sure enough: "you wanna see a real one?" Alberto asked.

"Alberto, no," said Luca. "We didn't see any humans, remember?"

"Yeah, you said you didn't see them," Harry agreed.

"We didn't see them today," Alberto replied, ignoring Luca's wild head-shaking, "but we've seen them before. In fact, we see them all the time! If you can help us stay good and wet and convince the grownups we belong here, we'll show you two humans!"

Harry looked suspicious. "You guys are in trouble, aren't you?"

"Of course not!" scoffed Alberto.

"Maybe a little," Luca admitted. They were going to have to get out of this place somehow, but they had no idea how to do that. Somehow they would have to stay safe until they could figure it out, and it was going to be a lot harder to stay wet here than it was to stay dry in Portorosso. They were going to need help, but he still felt like this was not the best way to get it.

"But you know where to find two humans?" Harry asked. "Real humans, not just pictures or people in Hallowe'en costumes?"

"Of course we do," Alberto said. "Cross our hearts. Right, Luca?"

"Yeah," said Luca, with less enthusiasm. "Promise."

"Okay," said Harry, "but if you can't deliver, I'm gonna tell my father you were sneaking around in his factory. Then you'll be in real trouble."

Luca swallowed hard, but Alberto patted Harry on the back.

"Don't worry," Alberto said. "You won't be disappointed."