The two mums agreed on a rota. They would each take turns driving Charlie and Anna to and from school. That meant no more walking to school in the rain or running home again from mysterious strangers. The two children were thrilled, but there was a serious reason behind it. The two mums phoned the school.

So in Thursday's assembly the headmaster warned the school about the danger of talking to strangers. He uncovered several large posters at the front of the hall and got people to put up their hands and pick out the strangers. Nobody picked the clown, the smiling old man or the footballer, but somebody picked the fierce policeman and was greeted with hoots of laughter.

"I know the answer," Anna whispered into Charlie's ear.

"Then put your hand up," he hissed.

She gave him a funny look, as if the thought hadn't occurred to her, then slowly raised her arm. The headmaster spotted it immediately and called her out to the front. She went up and started picking out the strangers.

"Stranger... stranger... stranger..."

She went along and pointed at every single poster, except the policeman.

Many of the children started to snigger and giggle. Des laughed cruelly from the back of the hall and Charlie glared at him. But as the headmaster went on to tell them, Anna had been absolutely right. A stranger is a stranger, he told them, no matter how nice and friendly they look.

Anna returned to her place smiling. Charlie pretended he had known all along.

Of course, it being Thursday, most of the children sat through the assembly dreaming of other things. It was the day before their outing, after all, and everyone was excited. Miss Broom came to the front to tell them what they would need to bring: a packed lunch, some colouring pencils and perhaps a few pennies to spend in the gift shop.

When the day of the museum trip finally arrived, everyone was in high spirits.

"We're all going on a summer holiday..." sang the children as the coach pulled away from the school and sped out onto the motorway. It wasn't in the slightest bit true, but they were all behaving so their teachers didn't complain.

Anna had got the window seat on the way there on the agreement that Charlie would get it for the journey back. They watched the countryside race by, though the coach had to make several unplanned stops for Emma and her carsickness. Des couldn't understand why she got carsick when they were on a coach, but Miss Broom told him to just sit back down and be quiet.

Des, however, had got bored of sitting quietly and was more interested in playing the fool. He had brought along some revolting joke sick and was throwing it into people's laps. Most of his victims found it hilarious, but Susan started shrieking. Mr Clayton got up and confiscated the sick, hiding it under his seat where it later fooled the driver.

By the time they eventually left the motorway and entered London, even the teachers were getting restless. The coach was hot and stuffy, and the radio wasn't working. Everyone was relieved when the coach finally pulled to a stop outside the gates of a magnificent stone building.

"The British Museum," announced the coach driver.

Everyone was glad to get off and stretch their legs, not least of all Miss Broom. She went back and forth, counting heads and striking ticks into her register to make sure they hadn't lost anybody before they had even arrived.

Mr Clayton disappeared into the museum to let them know they had arrived and returned a few minutes later with a very tall woman in tow. Charlie and Anna crept round to the front. They were both looking forward to this visit and neither wanted to miss anything.

Mr Clayton clapped his hands for them to be quiet.

"This is Mrs Bamber," he said. "She's going to be showing us around today."

Mrs Bamber was dressed in a very smart trouser suit and wore a pink pearl necklace. A pair of shiny new glasses swung around her neck on a yellow cord. As she stepped forward to address them she put them on.

"Welcome to the British Museum!" she said. "Are you all looking forward to your visit today?"

They all murmured that they were and then Mrs Bamber went on to explain the itinerary. Before lunch she would be giving them a whistle-stop tour of the museum. Then after they had eaten they would be splitting up into small groups to explore the museum's brand new mummy exhibition. That was what Charlie was looking forward to the most.

"So," said Mrs Bamber. "If you'll all just follow me, we'll begin..."

And then they were off. Mrs Bamber raced around the museum at top speed and the children fought to keep up. She barely stopped for breath as she took them to displays of old paintings, ancient pottery, exquisite jewellery and then sped off to another part of the museum.

Charlie and Anna didn't mind. They were enjoying the visit immensely. The same couldn't be said for the other children, however. As the morning progressed and the pace did not slow, they grew increasingly bored and tired.

"Bor-ring..." sighed Des under his breath as Mrs Bamber led them into yet another room of dusty old statues. Neither Mrs Bamber nor any of the teachers appeared to have heard, so Charlie gave him a dirty look on their behalf.

The next stop on Mrs Bamber's tour proved to be something of a highlight, however. It was a dim and murky exhibition of grisly old torture instruments and the children were fascinated. Des started making the girls squeal by making up horrid stories. Miss Broom came over and led him away by the hand.

Charlie was attracted to the stretching rack at the far end of the room.

Des managed to escape the clutches of Miss Broom and snuck up beside him.

"That's where they put freaks," he said, pulling a hideous face.

Charlie glared at him.

"Actually," said Mrs Bamber, appearing over their shoulders. "That's where they put rude little boys who won't do as they are told and stay where they are put."

Des gulped.

"Now," Mrs Bamber asked. "Is that bor-ring?"

Des shook his head, then slipped away quietly.

Mrs Bamber gave Charlie a smile and a wink. He grinned back at her. Evidently, she had heard Des after all. Then she went off to regale another group with more of her stories. Anna strolled over and turned her nose up at the stretching rack.

"They put people our age on this, you know," said Charlie knowledgeably.

Anna giggled. "No, they don't. She just said that to scare Des."

"Oh," said Charlie, feeling rather silly. "I thought so."

"No, they only put criminals on it, and they stopped doing that ages ago."

Charlie grinned sheepishly.

"How can anyone say history is boring?" wondered Anna.

Charlie had no answer for that question.

The pair of them caught up with Mrs Bamber once more and listed to her talk. Then it was down into the basement, where they could eat their packed lunches. Des and his gang fought their way to the front, but Charlie and Anna stayed back to listen to Mrs Bamber some more. By the time they arrived, there were only two places left.

One of them was on Des's table.

"Hey, Witch Girl!" Des called loudly.

"Come a sit with us, Witch Girl!" Roger crowed.

Sam and Eric cackled as they ate.

Anna groaned and looked up to Charlie.

"I'll sit with them," he said bravely.

So he did. He sat down next to Eric, facing Des who was sitting on the opposite side of the table, eating with his mouth open. The four of them made animal noises throughout but Charlie did his best to ignore them. He ate and rank far quicker than he ought so that he could escape them sooner.

However, as they ate, Des suddenly shot up his hand.

Mrs Bamber was passing and she stopped suspiciously.

"Yes?" she asked.

"Mrs Bamber," said Des. "Do you know anything about people with tails?"

"People with what?"

"Tails," he replied. "You know, like cats and dogs."

Mrs Bamber sighed. "You're being a silly light boy again, aren't you?"

And with that she turned her back and stormed off.

Des and his gang burst into laughter. Roger had a mouthful of food at the time and spat it out all over the table. Charlie was seconds away from lashing out at Des, but he knew that would make him just as bad a bully, so he didn't. Instead he tucked into his yoghurt with relish and tried hard to forget Des and his silly friends.

It wasn't long after that, however, that Miss Broom came over.

"Mrs Bamber tells me we have a very cheeky little boy over here," she said. "Now, I wonder who she could be talking about. Do you have any ideas, Des?"

"Charlie," he said quickly. The others all muttered in instant agreement.

"You liar!" Charlie snapped.

But Miss Broom hadn't been fooled.

"Des, Roger, Sam and Eric... when everybody else has finished eating you four will stay behind and clear up any mess on the floor. Do you understand?"

The gang looked horrified.

"But-" Des began.

"No," said Miss Broom, cutting him off. "No. I don't want to hear it."

Des sighed loudly. Miss Broom just walked away.

Charlie couldn't help himself. He broke out into a broad grin. Des fumed.

"I'm gonna get you, freak!" he hissed.

Before Des could wreak some fiendish revenge, Charlie scoffed down the last of his yoghurt and packed up his things. Then he went looking for Anna and found her sitting with Mrs Bamber. She was explaining to Anna why she found history so exciting.

"When we learn about history," she was saying. "It's like learning about another world. History's like a great story, full of action and adventure, with romance and heroes."

"But why do people find it so boring?" Anna wondered.

"Well," said Mrs Bamber, taking a moment to think. "Because it's different, I suppose. Some people have a hard time dealing with things that are different."

Anna sighed. "I know," she said quietly, watching Charlie approach.

Everybody was soon ready and raring to go, but then they had to wait for Des and his mates to clean up all their mess. Charlie and Anna took particular delight in watching the four of them walk around, grumpily picking up sticky sweet papers and apple cores.

When they finally got up the stairs and into the mummy exhibition, they found it had definitely been worth the wait. The entire floor had been designed like the interior of a pyramid, dark and creepy, with a maze of pathways leading between hundreds and hundreds of mummies and their caskets. Charlie stood back in awe.

Mrs Bamber took them to a few points of interest, including the mummy of a Pharaoh who had ruled all of Egypt many thousands of years before. His shrivelled form lay in a beautiful gilded casket and was decorated in fabulous sparkling jewels. Anna noted that he was the same height as Charlie and Charlie wondered how old he had been when he had died.

They stopped again by a bench in the centre of the exhibition. Mr Clayton slumped onto it and took the weight off his feet. Miss Broom sat down on the edge and started fanning her face with a guidebook. Mrs Bamber, however, offered to answer the children's questions. Anna had quite a few.

Once all questions had been asked, Miss Broom rose to her feet again.

"Now," she said loudly. "I want everyone to take a sheet or two of paper and find a mummy to draw. Split into pairs or groups of three and stick together. Mr Clayton and I will be wandering around, so no one leave this floor."

She went on for another minute or so, but she had already lost the attention of her pupils. They were chattering excitedly and drifting away into the dark corners of the exhibition. Charlie was looking forward to exploring it further himself.

An unruly line formed for the paper, with Anna and Charlie at the back.

As they waited in line, Charlie watched Mr Clayton separate Des from his gang. Once they had claimed their paper from Miss Broom, Mr Clayton sent Des and Roger off in one direction, and pointed Sam and Eric in another. However, as soon as Mr Clayton was looking the other way, the four of them met up again and ran off.

By the time Charlie and Anna got to the front of the queue there were only a few crumpled sheets left. They took them regardless and wandered out into the exhibition.

"Let's do the Pharaoh!" Charlie suggested.

Anna turned her nose up. "Everybody's doing that," she said.

"Well, what then?"

"I've got an idea," she said. "Follow me."

She led the way. Charlie felt lost as soon as they were out of sight of Miss Broom, but Anna seemed to know where she was going. She took him along a path that twisted and turned so much that just when Charlie was convinced they had travelled in a complete circle, he found they were in fact somewhere completely new.

"Here we are!" she finally announced, stopping abruptly.

Charlie looked through the glass of the display case and laughed. Propped up inside was a mummified cat and its casket. Charlie could only tell it had ever been a cat because it was labelled as such. Anna looked to him and frowned.

"What?" she demanded.

"It's boring," he said. "Let's do the Pharaoh."

"Oh, come on," she pleaded. "It'll only take ten minutes."

Charlie stopped and thought.

"More time to explore," she added.

That was enough for Charlie. He began to pull his pencils from his bag.

So they lay side by side on their stomachs in front of the display case, quickly sketching the cat mummy onto their crumpled pieces of paper. Anna had brought a few colouring pencils and so had Charlie, but they found they'd brought much the same ones, and neither had a blue. Charlie found he needed one.

"I'll go and ask Miss Broom," he said, picking himself up.

Anna didn't respond. She was too busy at work on her picture.

Charlie went off into the exhibition alone. He couldn't remember the way back, but he could hear Mr Clayton's distinctive voice in the distance and headed in that direction. He hadn't gone much further when the voices suddenly stopped and he quickly became aware of just how expansive this exhibition really was. There was not a soul in sight. There were just endless rows of mummies all around him.

The voices did not return, but Charlie retained a vague idea of their location. He continued in the same direction. He soon became aware of a clicking or tapping nearby and thought it was perhaps one of their group. When he found it getting closer he decided to check it out and turned a corner.

Charlie saw the man but the man did not see Charlie.

Charlie lurched backward and pinned himself to the wall. He did not dare move. He had recognised the man instantly. It was that same man he and Anna had passed in the park several days before. He was wearing the same long, black coat and that tapping came from the end of his walking cane.

He was getting closer and closer all the time and Charlie wondered whether he had been spotted after all. Charlie dared not breathe and dared not blink. He was, for that moment, as still as the mummies around him.

And then the strange man passed by and kept on going.

Charlie could breathe once more. He peered cautiously after the man. He seemed to be looking for something. It suddenly occurred to Charlie that the strange man's appearance was no coincidence.

The strange man was looking for them.

Though flustered, Charlie recalled what the headmaster had told them about reporting strangers. But that was not Charlie's first instinct. His first thought was of Anna because the strange man was heading straight for her.

As quickly and as quietly as he could manage, Charlie ran back to her. He slipped in and out between the mummies, darting from shadow to shadow, ensuring he went unseen. He found Anna still lying on her front drawing the cat mummy.

He called from afar.

"Anna!" he hissed. "Anna!"

She did not hear. She was concentrating too hard.

The tapping had stopped and the strange man was nowhere to be seen, so Charlie made a run for it. He skidded to a stop before her and squatted down, keeping an eye out for the man.

"Quick!" he said. "We have to go!"

She frowned and pushed him away.

"You're in the way of the light," she snapped.

Charlie snorted and snatched the drawing from under her. The corner tore off.

"Hey!" she barked angrily, grabbing it back.

"Listen!" he explained. "The man from the park is here. He's looking for us."

Anna stopped pulling on the paper. She started to pack her things.

"No," said Charlie, seizing her wrist. "We don't have time."

He pulled her to her feet and they ran together.

Charlie didn't know where they were going, and neither did Anna. All of a sudden the entire place looked unfamiliar, but Charlie could hear Mr Clayton talking in a loud voice once again. He seemed so much further away now. Charlie turned a sharp corner, pulling Anna behind him.

They froze.

There, not thirty feet away, was the strange man.

He had just seen them and frozen too.

"Charlie," he said.