"Mum? Josie next door has been captured by aliens."

Mum kept stirring the wooden spoon in the big bowl under her arm, as if she had someone in a wrestling hold and was doing serious damage to their brains. The sticky mixture inside made slick popping sounds. "Mm-hmm?"

Josh pushed his glasses back up to the bridge of his nose. "They took her up in a big, a saucer, a flying saucer."

"And are these aliens we should phone the police about or can you deal with them yourself?"

"I don't know."

"Well, have a think."

"Okay."

Josh went back out into the garden.

A couple of minutes later he was in the kitchen again, looking as breathless and serious as before.

"Mum?"

"Mm-hmm?"

"It's giants. Giant, um, monsters. They're creeping up the garden to get us. Hiding in the hedges."

"If they're hiding in the hedges, they can't be that giant, can they?" Mum said.

"Mm."

Josh watched his Mum tap the bowl with the wooden spoon. It gave a dull-sounding dong each time. He went back out into the garden.

This time it was barely a minute before he was back in.

He stood in the doorway that led between the kitchen and the back garden and looked at his mother with an intent expression. At the same time, he was shifting his weight impatiently from foot to foot.

"Josh, do you need to go to the bathroom?"

"Yes. Um, no."

Mum sprinkled flour over the mixture she'd spooned out of the bowl and started to roll it flat. Whenever a raisin stuck to the rolling pin, she picked it off and put it in her mouth.

"Mum," Josh said, breathing hard, "it's not giant monsters or aliens."

"Mm-hmm?"

"It's..." His face screwed up. "Bats. Loads of big bats. Vampire bats."

"And where are they, these bats?"

"I... I don't know."

He went back out into the garden again.

Josh stood on the step by the back door for a moment, wondering what to do. All those things he'd said weren't what he'd meant to say at all. He knew what he meant to say, but it wasn't coming out right. It was almost like, as soon as he found himself standing in front of his mother, what was in his head changed and he couldn't describe it properly, or the words he'd been meaning to use took on a different meaning as soon as he tried to speak them.

What could he do? He had to let someone know, and the only someone around was Mum.

He'd have to go and have another look. Perhaps then he'd be able to think of the right words. Really pin it down this time.

The garden was long, but it was thin. Once you'd walked halfway down, it angled slightly, so after that you were out of sight of the kitchen window. That was when you saw the shed. Dad had built the shed out of bits of wood he'd found in skips. For a long time, at first, there had just been this growing pile of scraps of wood at the end of the garden which had started to get on Mum's nerves. Whenever she saw it she'd say, "And when, exactly, are you going to build this shed of yours?" Dad would say, "I just need a few more big bits. The big bits aren't as easy to come by." For a while it had looked as though there wasn't ever going to be a shed, just a pile of mismatched planks and half-broken boards, making a home for spiders. Then Dad had found his last few big pieces all in one go and built the shed, with Josh there to hold the nail-tin and fetch the bits for the drill.

Josh didn't like being inside the shed because it was small and dark and full of creepy-crawlies. But he could get the ladder out, because the ladder was right inside the door, and you could use the ladder to get on the shed roof. Dad had said it was alright for Josh to get on the roof, but only while he was young. If he got any older, Dad said, the shed might collapse if he sat on it.

The roof was covered in tarpaper. From it, you could see into next-door's garden, both ways, and a few more next-doors the opposite way to Josie's. But also, if you were on the roof, you could see into the tangle of brambles and weeds that grew behind the shed, and then into the woods that backed onto all the houses. It was while looking into the woods that Josh had seen the thing he was trying to tell Mum about.

As he stood at the bottom of the ladder, he realised he wasn't at all sure he wanted to look at it again. The first time, he'd barely been able to take his eyes off it, and that was because of the real terror he'd felt, not because it was at all nice or interesting to look at. Now he was going to have to look at it again. How else was he going to find the words to describe it to his mother?

He clambered up the ladder and got onto the roof. In her garden next-door, Josie was lying face-down on a sun-lounger in her flower-print bikini, with the back of the top undone so she could get a full tan. She seemed to be asleep.

Knowing that, for some reason, it wasn't right for him, as a boy, to stare at Josie while she was sunbathing, Josh looked the other way, at the other gardens and the other backs of houses. He could see washing lines hung with bright white sheets, and greenhouses whose glass was choked with green, but there wasn't anyone else in sight.

He was going to have to be careful, then.

Gathering his courage, he turned round, in his sitting position on the shed roof, and looked into the thick mass of forest immediately behind the gardens.

It was still there. A patch of blackness hanging in the air. It was so dark that, staring into it, he saw purple blotches crawling at the edge of his vision, like it was sucking out the colour from all around it. It was so dark that cold air was seeping out of it — really cold, so cold it made your hands go white, even on a day like this. It was so dark it seemed to be pulling him in. He kept his hands gripping the edge of the shed behind him, because he knew if he fell into that patch of blackness, he'd freeze then fall forever into absolute nothing.

Josh began to shake. He had to get away from it, this awful, terrifying thing. But he also had to find the words to describe it, to tell his mother what it was. Because he was sure it was growing. He was sure it was getting bigger, getting ready to swallow the shed and the garden and the house, and all the other houses on the street, and then keep growing till it took in the whole world, freezing the people and sucking them in to fall forever, each one alone, into its infinite and absolute abyss.

But that blackness seemed to suck in the very words he needed to describe it. He stared at it as hard as he dared, gritting his teeth and demanding the words he needed, but they wouldn't come.

His hands began to slip. His face felt frozen and he couldn't turn his neck to look away. He heard the rasp as his shoes began to slide over the rough surface of the tarpaper roof.

With a shout, he turned and half jumped, half fell, off the shed roof onto the grass below. Then he was running back up the garden into the kitchen.

Mum was using a cookie cutter on the inch-thick rolled-out cake mixture. She glanced up as Josh burst in, hot and breathless and almost losing his glasses as he came to a stop.

He had to catch his breath.

Mum put another crinkle-edged dough cut-out onto the greaseproof paper-lined baking tray.

"Mum," Josh said.

"What is it, Josh?"

"It's... It's... It's pirates. No — bandits. Bandits in... in cars. Big beat-up cars. They're driving all over..."

He sagged.

"Would you like a glass of lemonade?" Mum said.

"Alright."

He gulped it down. He looked at his mother, as she calmly continued to cut shapes from the cake mixture. He realised this was something he wasn't going to be able to tell her about. He didn't have the words. That dark thing was going to grow and grow and swallow them all up, and he might have been able to warn them so they could do something about it, but he couldn't, because he didn't have the words.

"Would you like to play inside for a bit?" Mum said. "You must be getting hot out there."

"Alright."

He went upstairs to dig out his action man. Every so often, he went to the back bedroom and looked out the window at the garden, at the shed and the woods beyond it. He couldn't see the patch of darkness from here, but he wondered how long it would be till he could.