Thanks to their highly efficient magic bicycles and the incredible shortcuts known by Mortimer Grimalion, the professor and the children were quickly surrounded by London's dense fog near Euston Road, not far from the National Library.

They didn't have much time. Big Ben had rung its final strokes. That meant Pandèmiur Gobler could recover his powers at any moment and exit the Mirror of Abedhaar to complete his dreadful plan.

"I swear I've never seen a fog so thick in my life!" said Odilda, walking with her arms stretched in front of her toward something that looked like a front gate.

"It's like walking inside a giant cotton ball," said an amused Kate.

"Zis Krimor fog!" explained Grimalion, placing a cluster of mist inside his top hat. "Bevitcht fog. A vizart past by here."

"So, we are in the right place!" said Michael, walking in small steps to keep close to the postman.

"It reminds me of the fog I found once in Yakutsk, a remote place about 300 miles from the Arctic Circle," said Odilda, feeling the wall to find an entrance. "You know, a few years ago I got an urgent call from the director of a Swedish multinational specializing in large commercial excavations. While mining, his team found a huge black diamond that seemed to bring terrible misfortune and misery to anyone touching it. It was freezing cold. The thermometer marked -3 in broad daylight, and the fog... the fog, you guys, was so thick I could have sliced it and spread it on a bun."

"Please, can we not talk about food?" begged Michael, whose stomach had been demanding nourishment for hours. "I'm so hungry I could eat fried worms."

"This way!" shouted Peter. "The entrance gate is here!"

The professor, Grimalion, Kate and Michael rushed to the boy and began to knock loudly to draw the attention of the night guards.

"Anyone here?" shouted Peter. 

"Yoo-hoo!" called the professor.

"It's an emergency!" shouted Michael, shaking the railings. "Open up!"

Shortly after, they heard the clatter of a large bunch of keys and a muffled sound of footsteps approaching. Soon the door opened, showing the head of a sleepy caretaker with his cap turned sideways. "What's going on?" asked the guard, surprised to see children at this time at night.

"Odilda Costalbine!" the professor introduced herself with her practiced voice, showing her card issued by the Association of Paranormal Investigators. "We received an anonymous phone call," she said. Then she grabbed the guard by the collar and lowered her voice. "It looks like someone is going to steal something from the library... tonight!"

"Stealing? Here? Tonight?" said the guard skeptically.

"Exactly!"

"I'm sorry, but I don't know anything about it. Anyhow..." replied the guard, taking the professor's hand off his collar and staring at the strange group of people in front of him, "who in the world are you?"

"Listen!" intervened Peter, restless. "We don't have time to explain. You must let us in so we can call the police... RIGHT NOW!"

"You listen, little boy! If you don't leave, I'll be the one who calls the police!" replied the man, threateningly, as he pointed his torch to the boy's face. He then closed the door with three turns of his keys, and left mumbling something about scatterbrained parents who go around at night with their children to play stupid tricks on others.

"Mortals haf fery bad temper!" said the postman, still looking nervously behind him.

"Now what?" asked Kate, her hands on her hips.

"You try go in und I leaf!" said the postman, walking backwards.

"What do you mean leave?" exclaimed Odilda. "Do you want to leave us here by ourselves?"

"But you promised Egot you'd help us and protect us from danger!" said Michael.

"Not korrekt!" contradicted Grimalion. "I promise Egot I take you to destination und protekt you durink trip. I did it!" He swiftly jumped on the seat of his strange bycicle.

"But we can never make it alone!"

"Fery sorry..." said the postman, wiping his forehead with his arm. "Now danger für Mortimer. Blak sorcerer kumm any moment und... sssschwip!" He ran his index finger across his neck, mimicking the blade of a knife. "Kaput! End ov Grimalion!"

"At least help us to get in!" suggested Peter. "Help us to get inside the library, then you can go your way, okay?"

Grimalion looked pensive. Then, without saying a word, he stuck his gloved hand inside his worn-out doctor's bag.

"What's he doing?" whispered Michael in his brother's ear.

"I have no idea."

"I don't think he understood the question," said Odilda, looking at the man with almost a hint of compassion. "Let me try... um... herr Mortimer, kartoffeln sind gut und..."

"Ah-Ah... fount it!" exclaimed the man, holding a large silver knob. "I knew vas somevere!" he said, handing the object to Peter.

"Um... th-thank you...!" Peter replied, hesitantly.

"No problem!" answered Grimalion as he started to pedal. "Viz zis magik objekt you kan enter anyvere. But kareful... ven finischt, you kif bak to Grimalion, ja?" he warned them. "Break a leg... bad vizart's leg! See you!" The cheerful jingling of the bicycle's bell started to fade in the distance as Grimalion's large figure disappeared in the fog.

"How do you think it works?" asked Peter, turning the knob in his hands.

"Maybe we can find something in the book Egot gave us," suggested Odilda.

"Sure!" exclaimed Michael, eager to use some magic.

"Kate, look for a spell using a knob that can help us get inside the library!"

"Count it done!" replied the little girl, sitting on the floor with the big book on her lap. "Here it is!" she exclaimed, euphoric. "CHAPTER 4 – Spells and potions to enter, begin and start. Preparation: Melt a silver knob in a deep copper cauldron and cook together with one cup of bat saliva, one tablespoon of Vesuvius oil, three mustache hairs of a hibernating possum, 13 leaves of Great Mullein, one spoonful of caterpillar slime syrup, and..."

"Kate!" interrupted Michael, on the verge of exploding. "Look around. Do you think we can cook here? Besides..." he continued, turning his head left and right, "where do you think we can find three mustache hairs of a hibernating possum in London?"

"Right, because bat saliva and caterpillar slime syrup are everywhere!" added the professor, sardonically.

"Ok, ok! Don't get excited!" said Kate, moving her little fingers again through the yellowed pages of the fat tome. "Here! This section could do. Spells with the wand: point the magic wand in four directions - east, west, north and south, reciting the spell and focusing on the chosen destination. (Note - follow these instructions blindly). With two rounds of the ankle and a twist of the chin, on this wall you'll find the best way in."

"It does not seem that difficult!" exclaimed Peter, removing the wand from its wooden shell. The wand rebelled a little, then coughed a couple of times, leaving a trail of light in the air.

"Professor, be careful!" Michael warned her, as he drew the wand like a Wild West gunman. "I wouldn't want to shoot by mistake."

"Come on! There's no more time to lose," urged the professor.

The children lined up in front of the wall and tried to run the spell as explained in the big book. Soon, however, they discovered the art of witchcraft was anything but simple. At the first try, Peter's nose became longer. The second time, Michael grew a pair of horns on his head. The third time, Kate grew an extensive blond mustache. Only after a number of different attempts and at least a dozen other bizarre transformations the spell was executed to perfection.

"WITH TWO ROUNDS OF THE ANKLE AND A TWIST OF THE CHIN, ON THIS WALL YOU'LL FIND THE BEST WAY IN!" the children cried. Then they waited. Soon, the knob in Peter's pocket started to make strange noises, increasingly vibrating, until it darted away and attached itself on the first empty wall.

"Look!" exclaimed Kate, clapping for joy.

An Arab-style door topped by an arch entwined with tricolored strips appeared suddenly in front of them.

"Well done!" congratulated the professor as she neared the threshold. "Well done, indeed! When Michael changed into a plunger, I must admit I had almost lost all hope." She turned the knob, and instantly the whole group found itself inside the library.

"It's amazing!" exclaimed Michael, dreamy. "We could use this trick to go anywhere!"

"No, we can't!" scolded Peter. "You heard what Egot said. We have to use magic with extreme caution and very sparingly in the mortal world!"

"The usual killjoy!" grumbled his brother.

"So? Where do we start?" asked Odilda, wielding her whip.

"First, we should split up. We'll have more chances of finding the chimeria," suggested Peter. "I'll go this way with Michael," he pointed.

Odilda nodded, slashed the air with her whip, and went with Kate to the other side.

"Professor..." Peter called her back. "Please, be careful!"

"You should worry for the poor devil that crosses my path!" said the woman, winking and continuing to walk.

"Our treasure hunt has officially started!" said Michael.

The two brothers decided to begin with the reading room on the first floor.

"I don't know about you..." said Michael, following his brother, "but visiting places at night gives me the chills."

"Michael Moffet, you wouldn't by chance be afraid, would you?" Peter teased while looking around.

"Afraid? Me?" laughed his brother, still tense. "I'm just saying that in the dark things look different. That's all!" he explained, keeping his hand on the wand just in case.

They explored the room meticulously, walking through the endless row of desks and consulting libraries packed with books, looking for clues, but found nothing.

"They're not here!" said Peter "Maybe we sh..." "Wait!" silenced him Michael.

"What is it?"

"A noise!" said his brother, wide-eyed in fright. "Some sort of... scratching."

"I don't..." Just then, Peter heard a sound coming from the end of the hall. "W-what was that?" he asked, trembling, as he lifted his wand.

The noise seemed to come from a shelf in a corner of the large humanities section. It was as if someone was scraping his nails against something.

The brothers moved closer, slowly, holding their wands tightly in their hands. When they arrived, the noise stopped abruptly. Peter motioned to his brother to take a few more steps but Michael, of a quite different opinion, shook his head, pointing to the nearest exit. The battle of gestures lasted for a while and became so complicated the boys could hardly understand each other. Eventually, it was Michael who persuaded Peter to get closer to the shelf.

"I can't hear anything! Maybe it was just the wind against the windows," Michael whispered. "Can we go now?" he pleaded, eager to leave that place which, in the dim light of a few streetlights, looked somewhat ghostly.

"No! The noise came from here," replied Peter, placing his ear on a shelf. "I'm sure!" He then started to knock on the spines of the books with the tip of his wand: "Knock-knock-knock... knock-knock-knock..." until he received an answer.

"Knock-knock-knock!"

"Did you hear that? Someone knocked!" whispered Peter, excited. As he moved closer, he noticed a quivering book with a closed padlock and a thick, dark leather cover.

"And this is good news?" yelled Michael, raising his hands. "Someone or something is knocking inside a book. A-BOOK, Peter! Does that seem normal to you?"

"Knock-knock-knock-knock!" Peter knocked again, ignoring his brother.

"Knock-knock-knock-knock-knock!" replied whoever was in the book.

"Knock-knock-knock-knock-knock-knock!" the boy tried again, but was stopped by an angry voice.

"OK-OK! GET IT OVER WITH! Now, that we all know I'm in here, can you get me out, please?" asked a voice inside the book.

"Get you out? Not in a million years!" Michael replied to his disappointment, keeping his wand pointed forward. "First of all, we don't know who or what you are. Second, who can guarantee that once you're out you won't kill us?"

"Although I hate kids almost as much as the Christmas season, I've yet to do away with any of them, I swear!" the voice replied in its own defense. "Please let me out, I can't breathe in here!"

"Before we let you out, tell us what you're doing in there," asked Peter.

"Why am I here, you ask? Well, sometimes I like to be alone, to find myself after a stressful day at work. You know, in the dark, in silence..."

"Really?" said Michael, amazed. "Now, that's strange habit."

"NO, THAT'S NOT TRUE, PIGEON!" yelled the voice. "Someone has locked me up, I don't know how. I was working in my office and then... and then... I don't remember anything, except that I woke up in here. Please let me out!"

"Ok! But now, try not to get excited," said Peter pulling the large book out of the shelf. He read the title, Cagliostro's Prison.

"Maybe in this case Egot won't be upset if we use some..." Michael lowered the voice, "...magic!"

"Hurry, guys..." said the pleading voice. "There's hardly any air left in here!"

"All right! Let's see what the big book of spells suggests," said Peter, resting the two books on a table and lighting a nearby lamp. "Potions and infusions, hexes and charms, basic spells ... here we are! Spells of appearance and disappearance, transformation, levitation... spells of movement: to move something or someone from the present location. This might do the job! Execution: Twirl the tip of the wand in the air three times while saying the spell at the same time..."

"Let me try!" said Michael, pulling the book away from him and twirling his wand in the air: "ALIO TRANSFER!" he chanted, but there was no sign of the man imprisoned inside the book. Instead, Michael found himself instantly catapulted to the other side of the table.

"Wh-what happened?" asked the man in a choked voice.

"Don't worry. We're almost there!" Peter lied as he helped his brother get up. "Maybe that was not the right spell, after all!"

"You don't say..." replied Michael, rubbing his rump.

"How 'bout this?" asked Peter, pointing to another page.

"Unlocking spell... um... This time you try!"

Peter stood before the book and twirled his wand above his head. A ball of bright light grew on the tip of the wand and then moved with an incredible forward thrust.

"OBSTACOLA ABDUCE!" Peter said, directing the beam toward the padlock and causing it to open quickly, freeing the prisoner together with large clouds of dust.

"Cough-cough!" the man hit his chest with his fist. "I swear... I swear... Cough-cough... If I find out who played this stupid trick on me, I'll make him spend the worst fifteen minutes of his life," he said, dusting off his pants and turning a furious glance at the children. "What are you looking at? You've never seen a gentleman brush off his clothes?"

"No, no, it's just... it's..." started Peter, hesitant.

"You don't expect me to thank you, or even worse, reward you for saving me from that dreadful place, do you?" said the man, backing away and holding his hands close to his chest in fear. "By saving me, you've done your unquestionable duty as British citizens, and that's a reward in itself, you know?"

"Don't worry. We had no intention of asking for rewards," replied Peter, extending his hand. "My name is Peter Moffet and this is my brother Michael. We're the ones who have let you out of the book."

"Out of a book?" said the man, dumbfounded. "What are you talking about? Closed inside a book? Ridiculous!"

Peter and Michael looked confused.

"Um... excuse us, but... who are you?" asked Peter.

"Who am I? Oh, Lord, what am I forced to hear!" said the man, lifting his eyes. "I'm Isidore G. Dott, general director of this library, that's who!" He then blew on his shoulder to remove the last bit of dust. "I imagine you've heard my name."

"Never in my life," contradicted Michael.

"That's because you young people today are as ignorant as billy goats. By the way..." he continued, "can you explain what you're doing here at this time of night?"

"Do you want the long or the short story?" asked Michael.

"Never mind!" replied Isidore. "On second thought, I don't care about either!" He then stepped between the boys, grabbed them by the elbows, and dragged them toward the exit.

"Hey... wait a minute!" said Peter, struggling to get free. "Where are you taking us?"

"You can tell your story to the police. They'll certainly be interested in knowing how you've managed to get into my library, eluding our sophisticated alarm systems."

"No! Let us go!" yelled Michael, trying to resist. "We have to find something very important!"

"You can do your school research tomorrow morning," replied Isidore, unmoved.

"You're making a big mistake!" Michael forewarned him, still wriggling in an effort to get out of the man's grasp. "All human history could depend on what happens tonight!"

"Blah-blah-blah!" said Lord Dott, tired of the unbearable chatter.

"OK, but remember, you asked for it!" Michael threatened, pointing his wand at him.

"Put that weapon away immediately, you impertinent kid!"

"ALIO TRANSFER!" yelled Michael.

Dott was moved by an invisible force that pushed him inside a big umbrella stand and then thrust him, shrieking with fear, away from the large hall.

"That was brilliant!" complimented Peter, patting Michael on the shoulder. "Bloody brilliant! Now, we can finally continue with our search."

"Yes, but where?" asked Michael, discouraged.

"There!" said Peter, pointing to a plaque that read: "To the Gallery of Treasures."