'Go ahead, Mike.'

'At the bottom of the oceans – particularly the Pacific -there is a fortune in metallic ores in the form of small lumps lying on the seabed.' I took the half-nodule from my pocket and put it on the table. 'Like this lump here. There's no secret about this. Every oceanographer knows about them.'

Geordie picked it up and examined it. 'What's this white bit in the middle?'

'A shark's tooth.'

'How the hell did that get in the middle of a piece of rock?'

'That comes later,' I said impatiently, 'in the second lesson. Now, these lumps are composed mainly of manganese dioxide, iron oxide and traces of nickel, cobalt and copper, but to save time they're usually referred to as manganese nodules. I won't tell you how they got onto the seabed – that comes later too – but the sheer quantity is incredible.'

I turned to the atlas and moved my forefinger from south to north off the shoreline of the Americas, starting at Chile and moving towards Alaska. 'Proved deposits here, at the average of one pound a square foot, cover an area of two million square miles and involve twenty-six billion tons of nodules.'

I swept my finger out to Hawaii. 'This is the mid-Pacific Rise. Four million square miles – fifty-seven billion tons of nodules.'

'Hell's teeth,' said Geordie. 'You were right about incredible figures.'

I ignored this and moved my finger south again, to Tahiti. 'Fourteen million square miles in central and south-eastern Pacific. Two hundred billion tons of nodules. Like grains of dust in the desert.'

'Why haven't I heard about this before? It sounds like front page news.'

There's no reason why you shouldn't have, but you won't find it in the newspapers. It's not very interesting. You'd have to read the right technical journals. There's been no secret made of it; they were first discovered as far back as 1870 during the Challenger expedition.'

There must be a snag. Otherwise somebody would have done something about it before this.'

I smiled. 'Oh yes, there are snags – as always. One of them is the depth of the water – the average depth at which these things lie is over fourteen thousand feet. That's a good deal of water to go through to scoop up nodules, and the pressure on the bottom is terrific. But it could be done. An American engineer called John Mero did a post-graduate thesis on it. He proposed dropping a thing like a giant vacuum-cleaner and sucking the nodules to the surface. The capitalization on a scheme like that would run into millions and the profit would be marginal at one pound a square foot of ocean bed. It's what we'd call a pretty lean ore if we found it on land.'

Geordie said, 'But you have a card up your sleeve.'

'Let me put it this way. The information I've given you is based on the IGY surveys, and the one pound a square foot is a crude approximation.'

I stabbed my finger at the eastern Pacific. 'Zenkevitch, of the Soviet Institute of Oceanology – the Russians are very interested, by the way – found 3.7 pounds a square foot right there. You see, the stuff lies in varying concentrations. Here they found five pounds a square foot, here they found eight, and here, seven.'

Geordie had been listening with keen interest. 'That sounds as though it brings it back in line as an economic proposition.'

I shook my head tiredly. 'No, it doesn't. Manganese isn't in short supply, and neither is iron. If you started picking up large quantities of nodules all that would happen is that you'd saturate the market, the price would slip accordingly, and you'd be back where you started – with a marginal profit. In fact, it would be worse than that. The big metals firms and mining houses – the only people with the massed capital to do anything about it – aren't interested. They already run manganese mines on land, and if they started anything like this they'd end up by wrecking their own land-based investments.'

'It seems that you're running in circles,' said Geordie acidly. 'Where is all this getting us?'

'Have patience. I'm making a point. Now, I said there are traces of other metals in these nodules – copper, nickel and cobalt. You can forget the copper. But here, in the south-east Pacific, the nodules run to about 1.6 per cent nickel and about. 3 per cent cobalt. The Mid-Pacific Rise gives as much as 2 per cent cobalt. Keep that in mind, because I'm going to switch to something else.'

'For God's sake, Mike, don't spin it out too long.'

I was and I knew it, and enjoyed teasing him. 'I'm coming to it,' I said. 'All the figures I've given you are based on the IGY surveys.' I leaned forward. 'Guess how many sites they surveyed.'

'I couldn't begin to make a guess.'

I took a sip of whisky. They dredged and photographed sixty sites. A lousy sixty sites in sixty-four million square miles of Pacific.'

Geordie stared at me. 'Is that all? I wouldn't hang a dog on evidence like that.'

'The orthodox oceanographer says, "The ocean bed is pretty much of a piece – it doesn't vary greatly from place to place – so what you find at site X, which you've checked, you're pretty certain to find at site Y, which you haven't checked." '

I tapped the atlas. 'I've always been suspicious of that kind of reasoning. Admittedly, the ocean bed is pretty much of a piece, but I don't think we should rely on it sight unseen. And neither did Mark.'

'Did Mark work together with you on this?'

'We never worked together,' I said shortly. To continue. In 1955 the Scripps expedition fished up a nodule from about-here.' I pointed to the spot. 'It was two feet long, twenty inches thick and weighed a hundred and twenty-five pounds. In the same year a British cable ship was grappling for a broken cable here, in the Philippines Trench. They got the cable up, all right, from 17,000 feet, and in a loop of cable they found a nodule 4 feet long and 3 feet in diameter. That one weighed 1700 pounds.'

'I begin to see what you're getting at.'

'I'm trying to put it plainly. The orthodox boys have sampled sixty spots in sixty-four million square miles and have the nerve to think they know all about it. I'm banking that there are places where nodules lie fifty pounds to the square foot – and Mark knew of such places, if I read enough of his notes correctly.'

'I think you had a point to make about cobalt, Mike. Come across with it.'

I let my excitement show. This is the clincher. The highest assay for cobalt in any nodule has been just over 2 per cent.' I pushed the half-nodule on the table with my finger. 'I assayed this one today. It checked out at ten per cent cobalt – and cobalt, Geordie, is worth more than all the rest put together and the rocket metallurgists can't get enough of it!'* 2*

We ate Geordie's stew and very good it was, and by midnight we had just about talked the subject to death. At one stage I said, returning to a sore point, 'I wish I still had those notebooks. They were only rough working notes and Mark seemed to have gone up a lot of false trails – some of the assumptions seemed completely cockeyed – but I wish they hadn't been pinched.' '

Geordie sucked on his pipe, which gurgled. 'I could do with knowing why they were pinched – and who pinched them.'

'Then you agree that it has something to do with Mark's death?'

'It must do, boy. He got hold of something valuable…'

'And was murdered for it,' I finished. 'But who killed him? Kane? That's unlikely – it's an odd murderer who travels halfway round the world to inform the family.'

That was a good conversation-stopper. We were quiet for some time, then I said tentatively, 'If only we could get hold of Schouten.'

'He's on the other side of the world.'

I said softly, 'I think Mark came across a hell of a big deposit of high-cobalt nodules. He wasn't a bad scientist but, being Mark, he was probably more interested in the worth of his discovery – to himself. His theories were a bit startling though, and they intrigue me.'