Camping and caravanning had become an addiction with her, as she cheerfully admitted. A boyfriend had once persuaded her to join him in a package-tour holiday in Greece; the boyfriend had been satisfactory, but the confinement of hotel life had been less so. Her eyes had always been on the olive-studded hills and the emptier beaches, while his had been on the bars and the concrete swimming pools. She had liked him but she had been only briefly upset when six months later he had transferred his affections to a night-club hostess in Chelsea.

The following year she had gone alone, in her caravan, to those same hills and beaches; her love affair with the man had been consummated, but her love affair with Greece had not and she had been aware of the frustration all winter. She had driven home to London happy and she had never taken another hotel holiday.

In nearly forty years of camping, Miss Smith had learned a good deal. She knew what she could eat from the fields and hedgerows and what she could not; when she toured abroad – as she had done in places as far apart as Finland and Morocco – part of the fun was seeing how much of the same lore she could acquire locally. It tickled her pride that she could identify at least three High Atlas cacti which would enhance a couscous and two Arctic mosses which gave a unique flavour to soups. Such knowledge was gratifying but of course exotic; the British Isles were hei real field of study and she could do well for herself anywhere from the Fens to the Burren, from the Hampshire woods to the Sutherland glens. She could light and maintain a fire in a snowstorm. She could pick herbs to staunch bleeding, soothe headaches or ease constipation. She was an accomplished (and so far uncaught) poacher; she owned a licensed.22 rifle but she could hunt silently when discretion dictated. She disliked snares but had taught herself to use them and she had even had passable success with a catapult.

She did not object on principle to technical aids; her methane cooker was a beauty and she had a well-equipped medical cupboard; but she was wary of becoming dependent on them. She liked to feel she could manage if the gas gave out or the drugs could not be bought. Her little caravan library was strictly practical: road atlases, Culpeper's Complete Herbal, Black's Medical Dictionary, the caravan workshop manual and so on.

When Miss Smith had driven out of London into Epping Forest a week ago, she was only doing what she had done on more summer weekends than she could count (winter ones, too, come to that). But this time, from the start, the feeling was different. It was one thing to set off on a holiday of two or three days or weeks, knowing that the little house in Vicarage Road lay at the end of it, that minor extravagances were permissible, that whatever was used up could be replaced. It was quite another to accept that this was no holiday but the start of a new life-style, an open-ended journey that might never lead back to Vicarage Road. There were moments, in those first few days, when she asked herself if she was crazy. But her instinct told her otherwise, and in any case it was not Miss Smith's habit to brood on a decision once taken. So she slipped quite naturally into altered ways of thinking.

She must be careful with money, but not miserly because she might as well make the best use of it while it retained its value; and if she was right about the approaching crisis, the time might come when it was so much waste paper. She must reckon on becoming immobile when petrol disappeared from the pumps; but a full tank, and the jerrycans padlocked on her roof-rack, would take her almost a thousand kilometres, so she topped up the tank regularly. She kept on thinking of simple things that might run out. For example, it would be a pity to be reduced to stick-rubbing through lack of lighter flints… So at the next tobacconist's she bought a dozen packets which should last for years as she was a non-smoker, and four lighter-gas canisters. (She had two lighters, which had belonged to her father; it was not till weeks later that she discovered that one could buy Aimless lighters, which annoyed her; such a silly thing not to know.)

She busied herself with such thoughts and preparations but she saw no reason to be tense or solemn about them. While petrol could be freely bought, she was determined to have fun wandering.

She had kept moving in short daily hops, circling London to pick up the Thames above Reading, and then on to Savernake Forest, Avebury, Frome and the Mendips. Her westward move was not entirely planless. For one thing, she felt that before too long she should be basing herself somewhere in the Pennine area, because if petrol suddenly became unobtainable, the nearer she was to the centre of the island the more scope would her thousand-kilometre reserve give her; the wider the geographical choice one had, once the crisis took shape, the better. So she wanted to visit some of her favourite southern places before she settled down.

But a particular reason was that she wanted to go and see her only living relative, a young cousin who was a nurse in a hospital a few miles inland from Weston-super-Mare. Eileen was a sensible girl and Miss Smith felt that she, if no one else, should know what her eccentric middle-aged relative was up to.

It would be pleasant, Miss Smith thought as she came into Compton Martin, to go through Cheddar Gorge instead of taking the direct road. On this impulse, she swung south-west to cross the spine of the Mendips by the B 3371. It was a hot morning and Miss Smith sang to herself as the van climbed. She had happy memories of the Gorge and she wondered why she hadn't thought of this detour in the first place.

She might even put off visiting Eileen till tomorrow and spend the night near Cheddar. Yes, why not? She hadn't been down the Caves for years

She reached the junction with the B 3135 and saw the road block. It was manned by half a dozen soldiers and a sergeant was signalling to her to stop.

Miss Smith pulled-up, puzzled.

The sergeant asked politely: 'Where are you heading, ma'am?'

'Down the Gorge to Cheddar.'

'I'm sorry, ma'am – the Gorge is closed. You'll have to turn here and circle round through Draycott.' 'Oh, what a pity. Why?'

'A rock fall, after the tremors. It'll take some time to clear.'

'Well, I hope it's not near the Caves. You can reach them from the Cheddar end, I hope?'

'I'm afraid you can't, ma'am. The Caves are closed to the public. Routine precaution.'

The phrase 'routine precaution' aroused Miss Smith's suspicion at once. That old clichd… She said with deliberate innocence: 'Someone might have put up a warning notice at the crossroads back there, to save people wasting time.'

'I'll suggest it to my officer, ma'am,' the sergeant replied. Somehow Miss Smith felt that that was a cliche, too. She did not know why, but she sensed that the Gorge was being kept closed with the minimum of publicity… No, I'm being a suspicious old woman.

She smiled at the sergeant, and said, 'I think I'll turn back, then, and go on to Weston. No point in going to Cheddar if I can't see the Caves.'

The sergeant nodded and stepped aside. Miss Smith reversed into the fork, and swung round the way she had come, giving the sergeant a friendly wave as she left. He saluted her expressionlessly.

Am I being a suspicious old woman? she asked herself as she drove downhill again. Soldiers don't man road blocks. Police do… Though if there's been tremor damage round here (had the Mendips been mentioned? – she couldn't remember) perhaps the police are overworked and the Army's been giving a hand. Forget it. Enjoy the day.

But the question-mark stayed in the back of her mind all the way to Eileen's hospital.

She left the van in the car park and walked over to the main entrance. A red-haired young nurse grinned at her cheerfully from the admissions counter; Miss Smith had been going to enquire at the porter's lodge, but it was empty, so she crossed over to the nurse.