McAndrew did not answer, but picked up the blue notebook. He began to leaf through it, and this time he was occupied for much longer.

I didn’t speak, either. I had learned long ago that when McAndrew had that look on his face it was a waste of time to try to gain his attention. He was off in a different universe. Mary McAndrew must have learned the same thing, long ago in McAndrew’s childhood. She went off to the kitchen without a word and appeared a few minutes later with a loaded tea-tray.

McAndrew finally laid the notebook carefully back on the table.

“Well?” I asked.

“I dinna ken. It’s a thing a man has to sleep on.”

“That’s all you can tell us?”

“I can tell you what he — my father — wrote.” Mac said “my father” awkwardly, as though the words came hard to his tongue. “What I can’t tell you is whether what he wrote is true. That needs some hard thinking.”

“Nothing there,” Mary said. She calmly poured tea. “Nothing, just as I told you.”

It occurred to me that after leaving the contents of the box to rot for all these years she wanted there to be nothing.

McAndrew spoke again, slowly and carefully. “What Heinrich Grunewald says — what he says” — there was a slight emphasis on he — “is that there’s another way to produce compressed matter, and if ye do it his way there’s no need of electromagnetic stabilization. The compressed matter will be naturally stable. If he’s right, you can also achieve far higher densities than we have at present. Up to three billion tons per cubic centimeter.”

Mary did not react, but I did. The compressed matter used in the balanced drive plates averaged three thousand tons per cubic centimeter, and that was considered phenomenal.

“Does he say how to do it?” I asked.

“Aye. But that’s the hard bit to swallow. He says that it involves a local modification and enhancement of the strong force.”

“What strong force?” Mary asked.

I waited for someone to answer. Then I realized that unlike at the Institute, where bulging super-brains stood ready to lecture on any conceivable topic in physics, McAndrew and I were the only two available; and from the look on his face he was gone again, off to some unimaginable place where I could never follow.

“What strong force?” Mary said again. “Have the two of you gone deaf?”

“I’ll explain,” I said. I should have added, or try to. Make me your authority on physics and you run a considerable risk. “There are four basic forces in the universe.” That much I was sure of. “There’s gravity, that’s the one everybody knows even if they don’t understand it. There’s the electromagnetic force, that powers electrical motors and everything else to do with electricity and magnetism. There’s a thing called the weak force, which causes radioactivity.” (At that point McAndrew should have awakened and roasted me for a simplistic explanation. The fact that he didn’t meant he wasn’t really there). “And then there’s the strong force, which holds nuclei together when electromagnetic forces want them to fly apart.”

I was about to add that unified theories explained all four as part of a single generalized force, and that all were mediated through the exchange of virtual particles with names like photons and gluons. I didn’t. I could see Mary’s face.

I finished, a bit lamely, “What your husb — what McAndrew’s father claims to have done is find a way to change the way the strong force operates. If he was right, and he could make it stronger, then there could be a better way to form compressed matter.”

Mary sniffed. “If I’d known that was all I had in the box all this time, I wouldna have bothered to keep it all this time.” She picked up the video recording. “And here we have more of the same?”

“We don’t know yet.”

“So let’s take a wee look, and find out.” She went over to a corner of the living room and pulled back a drape to reveal a playback unit so antiquated that I’d have accepted the idea that it was steam driven. “Artie, are you awake? Artie! Och, the lad’s hopeless.”

“Play it,” I said. “Maybe it will bring him back into the real universe.”

“I have doubts of that. I never found anything that would when he’s got that face on him.” But she inserted the video recording.

The overhead lights, coupled to the playback unit, dimmed. The wall display flashed a brief kaleidoscope of color, then settled to show the figure of a standing man. It zoomed to a close-up of his face and I had a sudden and startling feeling of recognition. The long jaw and thin-lipped mouth were different, but the distant eyes and high, balding forehead were pure McAndrew.

Heinrich Grunewald spoke. His voice was slow, deeper than Mac’s, and slightly accented. “This recording contains its own time-line, giving the date and hour that it is being made. I’ll be away for a little while, so I want there to be no arguments regarding priority of invention when I return. I have developed a modified theory of the strong interaction, with huge and various commercial potentials. Among the near-term applications are cheap forms of compressed matter, the ability to make shipment of diffuse materials in much smaller containers, induced radioactivity, more compact forms of existing commercial fusion devices, and low-temperature proton-proton fusion.”

McAndrew was awake after all. I heard him gasp at that last item. Grunewald went on, “I am not talking theory alone. The technical details permitting each of these developments can be found here.” He raised a blue notebook, like a bigger version of the one in the lockbox.

I glanced at Mary McAndrew, who shook her head. “Nothing like that, not left with me. It’s been a long time, but I think maybe I saw it.”

McAndrew said, “Then where is it? We have no other lead.”

“It went with him.” I was surprised that the two of them were slow to catch on. “If it gives the practical details it’s worth an enormous fortune. He didn’t want to risk anyone else getting their hands on it.”

“We have to find it, and him.” McAndrew sounded unusually forceful. He saw my expression. “Oh, not the inventions, Jeanie. You know I don’t give a damn about them. We need the theory.”

Mary McAndrew turned to me. “I told you. He hasn’t changed a bit. He needs a keeper.”

I asked, “But where did he go?”

McAndrew snapped at us. “If the pair of you would stop blathering, maybe we’d have a chance to find out.”

Heinrich Grunewald was still talking. Mac reversed the video to the point where his father was hefting the blue book.

“… developments can be found here.” Grunewald flourished the notebook in a self-satisfied way and finally placed it back out of sight. “With industrial sabotage so common, I do not wish to perform my final validation experiments where others might find a way to steal or even to interfere.”

Mary McAndrew said, “Och, he’s crazy suspicious. He was always paranoid. I’ve never known another man look under every bed before he’d get in it, no matter who he was with and what he had to look forward to.”

McAndrew and I both shushed her, as Grunewald went on, “So to do the validation I’m taking the Fafner out, away from the main shipping lanes—”

“Got him,” I said.

“Keep quiet,” McAndrew snapped. But I’m a seasoned cargo captain, and for a change I knew something he didn’t. It didn’t matter whether or not Heinrich Grunewald told us anything else. If he had taken his ship out, as he said, then his flight plan would be on file. So would any firing of the ship’s engines.

The man was gone, but not forgotten and not untraceable. It might take a while, but I felt sure we would be able to track down McAndrew’s long-lost father.

Like many things in life, the problem I had been so sure I could solve proved more difficult than it sounded.