'It had better be coffee. I'd like to get stinking drunk but it wouldn't help.'

Philip turned on the light and got out of bed, stumbling wearily and crossly about the cubicle, burning his fingers on the kettle and swearing. They nursed their cups, sitting side by side on the bed.

‘What a future,' Philip said at last. ‘Me spending all day clambering about air-ducts, and you trying not to get beaten up, till the big quake comes. And then, God knows. Beehive should stand up to it but there's no telling.'

'Climbing about air-ducts,' Betty repeated, suddenly thoughtful.

Philip looked at her, puzzled. 'Keep me occupied, at least.'

'No, it's just… Darling – how big are those air-ducts?' 'The trunk ones – quite big. Anything from sixty centimetres to a metre seventy-five.' 'All the way to Surface?'

He caught her meaning, suddenly, and said 'Jesus!' 'Well?'

'Hang on a moment – let me think… Oh, God, it'd be crazy.' 'Crazier than staying here?'

'Darling, it could take hours… I'd have to work it out on my charts, of course – there'd be fans to bypass, filters to get through – it'd be murder. You'd never make it.'

'Could you?'

'I guess so – probably – but what good's that?' 'If you could, I could. I'm slimmer than you and I'm pretty tough.'

Philip was silent for quite a while before he said: 'We might just make it. You know what, darling? We might just make it.'

Betty took his empty cup from his hands. 'Right, then. Now perhaps we can sleep. And tomorrow, you get studying your charts.'

Two days later, they were ready.

The climb would be very hard work but possible. Even the vertical shafts would be easy to climb because the large ones they would be using were fitted with inspection-ladders. The problems would arise at the filters and fan-installations, of which there were several on the route Philip had planned. Some of the filters could be dismantled and replaced behind them, and all but one of the fans could be bypassed. But however they climbed, there were three places where they would have to emerge from inspection trap-doors into a corridor, and re-enter the duct through another trapdoor on the other side of the obstruction. They could have saved a lot of time by going directly via lift and corridor to the third of these open stretches, but that was ruled out because it could only be reached through areas for which Betty would have needed a special Security pass.

There was only one way to brave the open stretches; Betty must wear her maintenance uniform, and hope not to be seen – or at least not recognized – at those three perilous points.

They could take practically nothing with them apart from their anti-Dust respirators (compulsory at all times, in any case), all the money they had, and such small objects as they could stuff into their pockets. And, of course, the tools in the regulation maintenance kits they both carried – in Betty's case, as part of her disguise.

They debated whether it would be better to make their attempt during the day, or at night. Beehive corridors were swarming with the thousands of new arrivals brought in by the Beehive Red order, during the day; this would make busy maintenance workers less noticeable but on the other hand daytime meant a bigger danger of running into someone who knew Betty. In the end, they decided that four o'clock in the morning was the least risky time. Very few people would be about and anyone they did meet would surely accept that they were engaged in urgent work on the ventilation system; Philip was, after all, the official judge of that urgency.

Leaving their cubicle was a nervous business. Betty was still in her ordinary clothes, with her uniform in the shopping-bag. If they met anyone they knew, they could have been at a private party – but that shopping bag looked odd, they felt, and they were both very conscious of it. In the event, they met no one in the kilometre walk to the trapdoor they needed to start at, but there were still a few anxious minutes while Betty hid in a doorway till Philip had the trap open. They listened and she ran across. As soon as she was up the ladder a couple of metres out of his way, Philip came in after her and secured the trap-door behind them. Fortunately, they could be operated from both sides.

They climbed, against a steady and over-warm down-draught, for about a hundred metres till they reached a horizontal section of the duct. There, awkwardly in a sixty-centimetre space, Betty changed into her uniform – putting her other clothes in the shopping bag which had come with them till they found a suitable place to dump it.

They reached a filter, which took ten minutes to dismantle and replace – ten dirty and choking minutes, for the filter was excessively clogged. Philip caught himself making a mental note to find out why before he remembered that it was no longer his concern.

Just beyond the filter, they came to the first of their three danger-spots. A fan-installation had to be passed by emerging into a dozen metres of public corridor.

'Stay out of sight till I tell you,' Philip whispered, 'and for God's sake keep that torch out.'

He unfastened the trap-door and peered out. The corridor was empty, so he climbed through, propping the trap cover on the floor. Then he walked to the second trap-door and began to unfasten it.

Footsteps.

His heart in his mouth, Philip forced himself to carry oh naturally. A man rounded the corner and stopped, looking at him. He wore the police-blue of Security.

'Hullo,' Philip said, without stopping his work.

'Hullo… What are you up to, sir?'

'Bloody temperature fluctuations on Level Three. Director got me out of bed. There's something clogging a filter somewhere.'

'Tough… I'd better look at your ID, sir. Routine, you know. But everything's tightened up, since Beehive Red.'

'Sure.' Philip presented his card which not only identified him by name and photograph (a pity) but also gave his status of Senior Ventilation Officer (thank heaven). 'Hadn't the heart to get one of the lads up. They'd only just come off.'

'Thank you, sir.' The Security man gave him back his card and strolled on along the corridor to the other trapdoor. To Philip's horror, he stuck his head inside and pointed his torch about. After a few seconds he pulled his head out again, said chattily 'Never seen inside the ventilation – big, isn't it?', and moved away round the next corner.

Hardly believing their luck, Philip lowered the trap cover to the floor and hurried back to the first trap. When the Security man's footsteps were sufficiently faint, he called softly along the shaft: 'Betty? OK. Hurry.'

She slithered along the duct and joined him. He pointed to the second trap, and without a word she sprinted to it and disappeared.

When both trap-doors were back in place and he was beside her inside the duct, he whispered: 'How come he didn't see you?'

'Because I heard you talking and got back round the bend, stupid.' 'I love you,' he said, fervently.

Danger point number two passed without incident; nobody came near, and they were out and in again quickly. There followed a long and tiring climb, with several more filters to dismantle and replace, and a nerve-racking squeeze past a whirling fan whose bypass door was not really supposed to be opened unless the fan was switched off at the control room. Philip hoped the duty man was not awake enough to notice the temporary drop in air pressure which must be registering on one of his dials.

At last, a mere hundred metres from Surface, they reached danger point number three, the last and worst.

'Now let's recap the drill,' Philip whispered before he began unfastening the door. 'There's a good half-minute walk between this and the other door, so we can't do it like the first two. We have to play this for real, with you as my assistant. Out of this trap and re-close it; then walk naturally to the other one and open it, together. OK?'