Cocooned in the susurrating warmth from the heater and serenaded by the mournful beauty of Elbow's music drifting from the car's sound system, Jackie felt her eyelids drooping closed. She knew that uncurling herself from her seat and stepping out into the cold when they got home would be doubly horrible if she allowed herself to fall asleep, but she didn't care; she was warm and cosy and tired, and right at this moment that was all that mattered.

She was three-quarters asleep, the soft roar of the engine and the swirling music becoming part of her dream, when Joe said, 'That's strange.'

Reluctantly she opened one eye. 'What is?'

'This fog. It's appeared from nowhere. Look at it. It's like a barrier. Weird.'

Jackie had slumped down in her seat. She struggled upright and peered out through the windscreen. Blinked.

'That is weird,' she said.

The fog, thick and grey and impenetrable, seemed to stretch in a perfectly straight line across the road ahead. It stretched, in fact, as far as the eye could see in either direction, a smoky wall that bisected the landscape to left and right before dissolving into the darkness.

Almost unconsciously, Joe slowed the car to a crawl.

'It is fog, I suppose?' said Jackie. 'It's not something. . solid?'

'Course it's fog,' Joe snapped, then flashed her a look of apology. 'Sorry, love, it's just. . I'm a bit freaked by it, that's all.'

Jackie peered out of the passenger window, knowing that a few miles beyond the night-shrouded landscape were the even darker depths of the Bristol Channel. 'Maybe it's come in off the coast,' she said.

Joe made a non-committal sound. It was no kind of explanation, and they both knew it.

'Oh well,' he said, 'it is only fog, I s'pose. What's the worst that can happen?'

Without waiting for a reply, he pressed gently down on the accelerator and the car rumbled forward.