Wingstead said, 'Oh my God, Neil, I don't think we should do that.'

I was dumbfounded. 'What the hell's the matter with you, Geoff? I'm depending most of all on you. For God's sake stop being such a damned pessimist.'

I'd never let fly at an executive in front of his men before. But it was vital to keep morale high and a waverer at the top of the command line could ruin all our plans. He made a strangely listless gesture and said, 'I'm sorry, Neil. Of course I'm with you. Just tired, I guess.'

Zimmerman broke into the embarrassed silence. 'I don't think Geoff should go anyway, Neil. He's got enough on his plate already. Let me come instead.'

I was relieved. Damn it, I wanted Wingstead with me, and yet in his present mood he might be a liability. I wished I knew what was eating him.

'Suppose we succeeded, took the ferry. What then?' Hammond asked. 'Wouldn't their main force get to know about it?'

'Very likely, but they're at Fort Pirie and we'd silence radios and prevent getaways,' I said. 'The only thing we have to pray for is that the ferry is operative, and from what Kironji told me it's been in regular use recently so it ought to be.'

Then what?' Wingstead asked.

'We bring up the rig and get all the invalids on board the ferry, cram it full of people and shoot it across to Manzu. When it comes back we pile on as many vehicles as it can take, trucks for preference, and the last of the people. Once in Manzu it's a doddle. Get to Batanda, alert the authorities and send back transport for the stragglers. I bet they've got cold beer there.'

They chewed on this for a while. I had painted a rosy picture and I knew they wouldn't entirely fall for it, but it was important to see potential success.

Hammond stood up and rubbed out the sketch marks in the sand with his foot. 'Right – how do we start?' he asked practically.

Wingstead looked up, absurdly startled. His face was pale under its tan and I wondered fleetingly if he was simply afraid. But he hadn't been afraid back in the warehouse at Makara.

'I don't know,' he said uncertainly. 'I'd like to think about it a bit, before we start anything. It's just too -'

The hesitation, the slack face, were totally unfamiliar. Doubt began to wipe away the tentative enthusiasm I had roused in the others. Wingstead had cut his teeth on engineering problems such as this and he was deeply concerned for the safety of his men. I had expected him to back me all the way.

The problem solved itself. He stood up suddenly, shaking his head almost in bewilderment, took a dozen paces away from us and collapsed in the dust.

We leapt up to race over to him.

'Go and get a doctor!' Kemp barked and Proctor ran to obey. Gently Kemp cradled Wingstead whose face had gone as grey as putty, sweat-soaked and lolling. We stood around in shocked silence until Dr Kat and Dr Marriot arrived.

After a few minutes the surgeon stood up and to my amazement he looked quite relieved. 'Please send for a stretcher,' he said courteously, but there was one already waiting, and willing hands to carry Wingstead to the mobile hospital. Dr Marriot went with him, but Dr Kat stayed behind.

'I should have seen this coming,' he said. 'But you may set your minds at rest, gentlemen. Mister Wingstead will be perfectly all right. He is not dangerously ill.'

'What the hell is it then?' I asked.

'Overstrain, overwork, on top of the injuries he suffered in the plane crash. He should have been made to take things more easily. Tell me, did you notice anything wrong yourselves?'

I said, feeling sick with anger at myself, 'Yes, I did. I've seen him losing his drive, his energy. And I damned well kept pushing at him, like a fool. I'm sorry -'

Kemp cut me off abruptly.

'Don't say that. I saw it too and I know him better than anyone else here. We must have been crazy to let him go on like that. Will he really be all right?'

'All he needs is sleep, rest, good nourishment. We can't do too much about the last but I assure you I won't let him get up too soon this time. I might tell you that I'm very relieved in one respect. I have been afraid of fever – cholera, typhoid -any number of scourges that might strike. When I heard that Mister Wingstead had collapsed I thought it was the first such manifestation. That it is not is a matter of considerable relief.'

The Doctor's report on Wingstead was circulated, and the concern that had run through the convoy camp like a brush fire died down.

I found Hammond. 'I want to talk to all the crew later this evening. The medical staff too. We'll tell them the whole plan. It's risky, but we can't ask people to work in ignorance.'

Then I went to find Sam Kironji.

'Sam, what's in that little hut inside the compound?' I asked him.

He looked at me suspiciously. He'd already found the compound gate unlocked and Harry Zimmerman and two others counting empty drums, much to his disgust. 'Why you want to know?'

I clung to my patience. 'Sam, just tell me.'

There was nothing much in it. The hut held a miscellany of broken tools, cordage, a few other stores that might be useful, and junk of all sorts. It was where Sam put the things he tidied away from everywhere else.

I made a space in the middle of it, had Kironji's desk brought in, and established it as my headquarters. The roadside cabin was too far from the camp and too exposed. Some wag removed a Pirelli calendar from the cabin wall and hung it in the hut, and when Kironji saw this I think it hurt him most of all.

'Stealers! Now you take my women,' he said tragically.

'Only to look at, same as you. You'll get them back, I promise. Thank you for the desk and the chair, Sam.'

He flapped his hand at me. 'Take everything. I not care no more. Mister Obukwe, he fire me.'

Hammond was listening with amusement. 'Never mind, Sam. If he does I'll hire you instead,' I said and hustled him outside. I sat down and Hammond perched on the end of the desk. We each had a pad of paper in front of us.

'Right, Ben. This is what I've got in mind.'

I began to sketch on the pad. I still have those sketches; they're no masterpieces of the draughtsman's art, but they're worth the whole Tate Gallery to me.

Take an empty drum and stand it up. Place around it, in close contact, six more drums, making damn sure their caps are all screwed home firmly. Build an eight-sided wooden framework for them, top, bottom and six sides, thus making a hexagon. No need to fill the sides solidly, just enough to hold the drums together like putting them in a cage. This I called the 'A' hexagon, which was to be the basic component of the raft. It had the virtue of needing no holes drilled into the drums, which would waste time and effort and risk leaks.

How much weight would an 'A' hexagon support?

We got our answer soon enough. While we were talking Sandy Bing reported breathlessly to the office. 'Mister Mannix? I got forty-three and a half gallons into a drum.' He was soaking wet and seemed to have enjoyed the exercise.

'Thanks, Sandy. Go and see how many empties Harry Zimmerman has found, please.' Zimmerman and his team were getting very greasy out in the compound.

The drums were forty-two gallons nominal but they were never filled to brimming and that extra space came in handy now. We figured that the natural buoyancy of the wooden cage would go some way to compensate for the weight of the steel drums, and Bing had just handed me another few pounds of flotation to play about with. We decided that my 'A' hexagon should support a weight of 3,000 pounds: one and a half tons.

But there wouldn't be much standing room. And a floating platform about six by five feet would be distinctly unstable. So my next lot of figures concerned the natural development upwards.

All this would take a little time to produce but it shouldn't be too difficult. Testing the finished product as a floating proposition would be interesting, and finding a way to push it along would stretch a few minds, but I didn't really doubt that it could be done. And the final result, weird of shape and design, was going to win no prizes for elegance. I jiggled with a list of required materials; some of them were going to be hard to find if not impossible. All in all, I couldn't see why on earth I was so confident that the plan would work.