The outskirts of Musselburgh were already congested with pedestrians, mostly, it seemed, fleeing as she was to the east. The tophra fall, thick now as a black snow, made it gloomy, and people were groping their way along with flashlights and umbrellas. Most of them had shirts or pieces of cloth fixed over their faces. She passed one woman who looked to have been overcome by an asthma attack; a doctor was attending her with an inhaler and what was probably a steroid shot, something to keep her moving.

Out of town, the traffic moved freely at first, and as they achieved more distance from the city, the tophra fall thinned out. But the A1, the road east out of Musselburgh, was a car park.

So Jane swung north at Tranent, and hit the coast at Port Seton. The power station here, chimneys and boxes of corrugated iron and glass, was still working.

Then she followed the coast road to Longniddry, and then through Aberlady across the bay to the A-road that led to North Berwick.

The traffic was moving on the coast roads, but it was almost solid. One bad accident, a single burst radiator, would clog up the whole damn thing. Her son’s critical path to safety was littered with the dodgy cars and lousy driving of thousands of panicky strangers. Terrific.

Every radio channel was given over to news and evacuation instructions, and she turned it off. There was one music tape in the car which she played over and over, as the car limped on.

She knew the coast well from her own childhood. It was a peaceful place, beaches and caravan parks and golf courses, a place where families came to spend time together. Day trips, sausage sandwiches and tea and cake in little cafes.

Here was Jack’s childhood: grimy, underfed, in mild shock, huddled into a car seat, clutching a battered sycamore-shape spaceship to his chest, eyes as wide as saucers. It worried her that he’d barely said a word for days. But she would have to think about that later, when she had secured his survival.

It wasn’t so far. Fifteen or twenty miles to Dunbar. She had plenty of petrol. If she could do it she would run as far as Berwick-upon-Tweed, the first big coastal town to the south, inside England. Surely they would be safe enough there.

But they had to get there first.

She tried not to look back, at the orange glow and palls of smoke and lightning that played to the west. She tried not to think of her father, or Mike, or Henry. There was nothing she could do for any of them now, or they for her. Time enough for them later.

For now, Jack was her whole world.

The ground shook, every few minutes; she could feel it through the car’s suspension.

The car edged forward.