Charlie's mum was most alarmed. As she drove him home she quizzed him about it, asking the same questions over and over. What did he say? What did he do? What did he look like? Charlie gave the same answers each time but she still kept on asking them.

When they finally got home his mum went straight to the phone before she'd even removed her coat. She called the police and told them everything Charlie had said. They told her they couldn't arrest people if they hadn't done anything wrong. They added that they'd keep an eye out for any suspicious characters but Charlie still had to listen to her complaining about it all through dinner and well into the evening.

The next morning, Charlie bent the truth once more.

"Where are you going?" his mum demanded.

"Just Anna's," he told her. "Her mum will be there, so it'll be safe."

"Hmm," said his mum. "I suppose that's okay, then."

So she let him go. It wasn't really lying. He'd just left some of it out. He was going to Anna's house and her mum was going to be there. What he didn't tell her was that they wouldn't be staying for long and would be going off to the park alone.

If she had known the whole truth she would never have let him go, but nothing was going to get in the way of their plans. Anna had phoned him up excitedly after dinner and told him about a huge tree she had spotted out of her bedroom window, which overlooked the park. It would make a perfect base, she assured him.

So early on Saturday morning Charlie turned up at Anna's house and rang the bell. Her mum answered. As Charlie learnt later, Anna had told her mum all about Des, but nothing about the strange man, and that was why she didn't mind them going out by themselves.

Anna came bounding down the stairs.

"Hi, Charlie," she called. "Bye, mum."

Her mum waved from the door as they headed off down the road.

"Fort Freak!" said Anna suddenly as she led Charlie across the park.

"Eh?" said Charlie, giving her a funny look.

"That's what we can call our base," she continued. "Fort Freak."

"Umm, why?" he wondered.

"Well, if we're the Freak Gang, then it's the perfect name, isn't it?"

Charlie shrugged. It would do until he came up with something better, he supposed. Of course, when he finally saw exactly which tree she had in mind, he couldn't care less what they called it.

"Wow!" he exclaimed, taken aback.

The beech tree was undoubtedly the finest tree in the entire park. It was a towering monstrosity, bursting up through the soil and soaring skyward, with lots of long, twisting branches and a thick, dark plumage of rustling leaves. The tree was taller than a house and its bark was as hard as stone.

"It's perfect!" he cried, looking to Anna with a grin.

So they set about building Fort Freak around the tree. They had dragged a cardboard box between them all the way from Anna's house and now she set to work making this into their wall. She sliced down one edge with a pair of scissors and started folding and bending it this way and that.

Meanwhile, Charlie whistled whilst he squatted down and scrabbled in the dirt, brushing away all the dead, wet leaves that had fallen from the branches above. He swept them all into a pile and then flung the pile out over the bushes. The leaves scattered in the breeze, but at least they were out of the way now.

Charlie dusted his hands off on his jeans and went over to Anna's side.

"Right," she said. "Take the other end."

Charlie seized one end of the cardboard wall. It was catching the wind and flapping back and forth like a sail. It needed the two of them just to hold it still whilst Anna moved it slowly into place.

"Okay," she said slowly. "Let go."

They both let go and took a step back. For a moment the wall stood firm. But then the wind caught it and it flopped right over. They both burst out laughing.

"Here," said Charlie, dropping to the ground.

He started to pick up the muddy pebbles.

"If we get enough of these," he continued. "We can wedge it into place."

Anna agreed, so they spent the next few minutes ducking in and out of the bushes, coming back every now and then with hands and pockets full of pebbles. Soon there were none to be seen but those on the pile. They had more than enough, so Anna set to work on wedging their wall into place.

"This is going to be brilliant," she claimed as she worked.

Charlie couldn't agree more.

"What about a moat?" he wondered.

"A moat?" she sniggered.

"Yeah," said Charlie, pulling his mum's hand trowel from his bag. "A moat."

He began to dig.

Anna just shrugged and finished arranging the pebbles. Whilst Charlie dug, she disappeared back into the bushes, returning a short while later with more sticks than she could ably carry. She put them down before she dropped them, then set to work reinforcing the cardboard wall with them.

The base was beginning to take shape. There was the mighty beech tree at its centre, Anna's wall on one side, Charlie's moat on the other, and where there was neither wall nor moat, there were prickly thorn bushes. Des would have a hard job breaking through their defences, Charlie reckoned, even if their moat was only a few inches deep.

"I'm thirsty," said Charlie sometime later.

Anna stopped and admitted she was too, so they sat themselves down within the walls of Fort Freak and had a drink. Charlie had sneaked a large bottle of lemonade from the fridge back home and Anna had brought a large bag of juicy grapes. They shared both between them.

They were too busy filling their mouths to speak, but Charlie caught Anna giving him fleeting glances. However, whenever he looked up, she looked away. It didn't bother him at first, but soon he just had to ask.

"What's up?" he said.

Anna looked startled, as if she hadn't been expecting it.

"N-nothing," she stammered.

Charlie frowned. "Come on," he probed. "Why the funny looks?"

She sighed, turning a grape over in her fingers slowly.

"I wanted..." she began.

Charlie waited.

"Can I..." she continued, only to stop once again.

"Yes?" asked Charlie.

Anna squirmed. She took out another grape and ate it slowly, nibbling off the skin and then sucking the juicy flesh. All the while, Charlie sat there wondering what could possibly be the matter.

"This is going to sound really strange," she finally groaned.

Charlie grinned.

"Well," he said. "This is Fort Freak and we are the Freak Gang."

She smiled nervously.

"Charlie," she said. "Can I ask you something?"

"Sure," he shrugged, popping a grape into his mouth. He was actually quite surprised. Anna was so much brainier than he was that he couldn't begin to imagine what she would need to ask him about.

When she spoke again, she spoke very quietly.

"Charlie," she said. "Can I see your tail?"

Charlie was taken aback. That was the last thing he had been expecting and he didn't know quite what to say. Anna began to squirm once again.

"It's just..." she began again. "I never saw it properly..." Charlie paused, unsure what answer to give. This wasn't a sum, where there was a right or wrong answer. He had to decide for himself.

Anna bowed her head and started picking at her shoe.

"I'm sorry," she muttered. "I shouldn't have asked. It was rude."

Charlie shook his head, rolled his eyes and sighed.

"Oh, why not?" he said and stood up.

Anna stood up as well and folded her arms nervously. "Really?" she said.

"Sure," he said, loosening his belt several notches.

As Anna looked on, he leant forward, shuffled around, bent over and pinned back his trousers with the crook of his thumb. Charlie noticed she was trying to hide a smile behind her fingers, but he realised he must have looked pretty funny anyway.

Charlie took a deep breath and with his heart pounding, he pulled out his tail and turned round. Anna said nothing. Charlie knew she wouldn't scream or run away or anything, but he was expecting her to say something.

"Anna?" he whispered.

Still she said nothing. She was right behind him. He could hear her breathing, but he couldn't see her face. Charlie had had enough of this silence, so he swished his tail from side to side. It caught her on the arm and she burst out laughing.

Charlie spun on his heel and joined in.

When she'd finally calmed down, she said, "It's a very nice tail."

Charlie's face dropped instantly. "It's not normal," he muttered.

Anna rolled her eyes and threw up her hands. "Who cares?" she cried.

Charlie didn't need to think about that answer.

"Des," he spat.

"Des," Anna said loudly, "is not normal!"

Charlie laughed once again. As usual, she was right.

"Here," he said, crouching down. "I have something else to show you."

Anna knelt down beside him and peered into his rucksack as he rummaged around inside. He brought out a pair of shiny black binoculars and her eyes widened. They weren't a cheap, plastic toy pair. These were the real thing.

"Charlie," she said. "Do you know how much these things cost?!"

He nodded. "They're the best money can buy," he said proudly.

"Does your mum know you've got them?"

Charlie nodded again. "They're mine. My dad got them for me before he left."

"Oh," she said, blushing.

"Here," he said, handing them over. "Take a look."

Anna lifted them to her eyes and began twiddling the dials.

"Wow," she said slowly. "I can see my house from here."

Charlie grinned. "Why don't you climb the tree and get a better view?"

She lowered the binoculars and shook her head.

"No thanks!" she said. "Here, you go and have a look."

Charlie stood once more and slung the binoculars around his neck. He started climbing the tree, going from branch to branch, using knots in the wood to pull himself up. It wasn't a particularly hard tree to climb, but the higher he went, the thinner the branches became and he wasn't sure they could support his weight.

When he had climbed as high as he was able, he perched himself upon a branch and locked his legs around the trunk. Then he raised the binoculars once more and brought them into focus. He started panning across the park.

He could see the gleeful smiles on the faces of the children on the swings. He could see the label on the packet of bread from which an old couple was feeding ducks by the duck pond. It was as if he was standing beside them, yet he was invisible. It felt naughty, but also exciting!

"Can you see anything?" Anna called.

Charlie ignored her. He was watching the old couple with a smile. They had just dropped their packet of bread in the water and were trying to fish it out with a stick. Suddenly a dark figure reached out and rescued it for them.

Charlie almost dropped the binoculars in shock.

For a moment Charlie lost sight of him, but then the strange man came back into view. He was wearing the same black coat he had been wearing at the museum, and he was carrying that silver-topped cane again. He handed the bread back to the old couple, and then moved away. Charlie followed his every move.

"What do you see?" Anna called, louder this time.

Charlie continued to ignore her. The strange man disappeared behind the bushes and Charlie lost him. He zoomed out to get a wider view, spotted him again amongst the trees and zoomed back in. The strange man stopped and looked around. Then he changed direction and started back the way he came.

"Charlie!" Anna shouted.

But Charlie was fixated. The strange man was looking for him. Of that, Charlie had no doubt. He dared not lose sight of him. But what he did next chilled Charlie to the bones. He turned his head and for a moment Charlie thought he was staring right at him. This time he did drop the binoculars. They fell slack against his chest as he began a hasty descent down the tree. It seemed so much higher on the way down, but he did not stop until his feet were firmly on the ground.

"Charlie," said Anna quietly. "You've gone all white!"

Charlie was breathing heavily. "It's him. He's here."

"W-what?" she stuttered.

"It's that man again," he told her. "He's in the park!"

Anna frowned and looked around cautiously.

"Did he see you?" she asked.

Charlie shook his head.

"No," he said. "I thought he did, but he couldn't have. It was too far."

Anna nodded. "Well, then," she said. "This is the perfect opportunity."

"To do what?" he wondered.

"To spy on him," she replied. "Do a little detective work of our own."

Charlie turned his nose up at that idea.

"I don't know," he said. "It sounds dangerous. We should call the police."

"No," she said, shaking her head. "He'll be long gone before they get here."

Charlie wanted to disagree. He remembered everything that his mum and Miss Broom and the headmaster had told them about strangers. He knew it was dangerous and he wanted to tell Anna that. However, when the time came to speak, he couldn't help but agree with her.

"Alright," he said. "This is our chance."

Then he tucked his tail back into his trousers and tightened his belt.

The two of them snuck across the park, keeping to the shadows and hiding behind walls and trees. This was Anna's plan and Charlie merely followed. When they reached the duck pond, however, the strange man was nowhere to be seen. They looked all over for him, but he had completely vanished.

Charlie was afraid. When he could see the strange man but the strange man couldn't see him it had been exciting. But now they couldn't see the strange man and there was every possibility he was watching their every move it was scary.

He looked to Anna. She didn't look scared. She looked disappointed.

"We lost him," she sighed.

Then a soft voice behind them said, "Are you lost, honey?"

Charlie and Anna turned. The old couple that he had seen feeding the ducks stood there. The old man was holding the bread packet up and letting it drip dry, but the old woman was smiling at the two of them.

"N-" began Charlie, but then Anna stood on his foot.

"Yes!" she said loudly. "Have you seen my dad?"

The old woman paused for thought. "Did he have a funny walking stick?"

"Yes," cried Anna again. "That's the one!"

The old woman began looking around.

"Oh, he was here just a minute ago..."

"Did you see where he went?" asked Charlie.

She tapped her lips with a finger. "I think he was heading for the car park."

"Thanks," said Anna, smiling sweetly.

"Bye," Charlie added, then the two of them took off.

They followed the path around the duck pond and then left the path and took a shortcut through the flower gardens. They weren't supposed to be there without an adult so were chased out of the other gate by a gardener. They'd still managed to cut their journey in half, however, and by the looks of it, they had arrived before the strange man.

"I don't see him," said Charlie loudly.

"Shhh!" Anna hissed.

Then she took hold of his sleeve and pulled him down behind the bushes with her. They peered between the leaves and branches, into the car park. There were quite a few parked cars, and quite a few people getting in or out of them. None of them were their man.

Charlie began to tap his foot nervously. He checked his watch. Even if the strange man had taken the long route round he still should have got back by now. He looked to Anna. She was frowning.

"What if he wasn't coming back here after all?" he whispered.

Anna glared at him momentarily then returned to her spying.

Suddenly she gripped his arm and made him jump. She pointed, and sure enough, the strange man was coming along the side of the football field. Charlie pressed himself into the bushes. If the strange man continued on this route, he would pass them by on the other side of the bush.

"Make... no... noise..." Anna mouthed.

She had noticed what he was doing and had flattened herself against the bush.

Holding his breath and peering between the branches, Charlie saw the man walk past, glancing from side to side shiftily. If it had been anyone else, Charlie would have thought he was simply admiring the view.

They listened to his footsteps grow quieter and quieter and then disappear.

"Quick!" Anna squealed, leaping up.

Charlie jumped up beside her.

The strange man was climbing into a big black car at the far end.

"Come on!" said Anna, and dropped to her hands and knees.

Much to Charlie's alarm, she started crawling out of their hiding place and into the car park itself. He thought this completely mad, but he couldn't let her go on her own, so scurried after her.

She finally stopped behind a large white van, which was parked right next to the big black car. She stood up, back against the side of the van and waited for Charlie to join her. He rose to a crouching position and hurried over.

Both of them were breathing heavily. Anna was trembling with excitement.

They waited here as the big black car purred to life and drove away.

"Quick!" Anna cried. "The registration number!"

They leapt out of hiding and gazed after the car, but it was already too far away. Anna groaned loudly, but Charlie already had an idea. He put the binoculars to his eyes and brought them quickly into focus. He zoomed in fast on the escaping car.

"TA1..." he read. "L5."

"TA1 L5!" Anna cried. "You got it!"

She jumped up and down on the spot and threw her arms around Charlie. He grinned from ear to ear and then the car went out of sight.

"Quick," he said. "Let's go home and tell the police."

Anna nodded.

They walked through the park with big grins on their faces. Charlie felt like this was a great achievement. Neither of them spoke, but he just knew Anna was thinking the same. As they began to cut across the football field, Anna held Charlie back.

"Look," she said menacingly and pointed over to the other side.

Charlie followed her finger. She had spotted four boys of their size larking about with a piece of rope in amongst the trees. She had spotted Des and his gang. Charlie gulped.

"Let's go the other way round," she suggested with a sigh.

Charlie shook his head.

"No," he said sternly. He was in too good a mood to run away from Des this time. "I have a much better idea."

Before Anna could ask what, he pulled his tail right out of his trousers and started running. Des and his gang didn't see him at first, but when they did, they stopped what they were up to and just stared.

Charlie pulled the most hideous face he could and started making loud gorilla noises. Des was taken aback. Charlie hunched his shoulders and began swinging his arms back and forth. When he entered the trees he reared up and started hollering and beating his chest.

"Run!" screamed Des and the whole lot of them scarpered.

Charlie chased them for a while, but he soon found he was laughing too hard to keep up. When Anna finally caught up with him she had seen it all and was laughing too. They stood there chuckling for several minutes before heading home, guffawing all the way.