I heard the door at the back of the room open. Jarver was coming back in, and Lyle and Parmikan dutifully hurried back to his side. I shivered, and sat up straight in my seat. Something creepy had brushed by me in the past few minutes, and I didn’t yet know what it was.

“So that’s it,” McAndrew was saying from the podium. “The two best candidates for the missing material needed to flatten the universe are hot dark matter — probably energetic neutrinos with a small rest mass, generated soon after the Big Bang; or maybe cold dark matter, particles like the axions needed for charge-parity conservation, or the photinos and other more massive objects required by supersymmetry theories.

“So which should we believe in, the hot or the cold? We don’t know. They both have problems describing the way that the galaxies formed.

“Worse than that, we aren’t measuring nearly enough of either kind of matter. Add everything together, and we still have less than half the mass density needed to make a flat universe. We must be badly underestimating either the cold dark matter or the hot.

“Which? Theory still can’t provide the answer. Most of the events that decide all this began happening in the first 10^-35 seconds after the origin of the universe, when we weren’t around to do experiments; when even the laws of physics may not have been the same.

“We may never know the composition of the missing matter, until we can put our instruments in the right place for observation — deep in interstellar space.”

He halted. Siclaro nodded his appreciation, and Mac came ambling back to his seat.

Naturally, he had missed the whole interaction with Lyle and Parmikan. He’d have missed it even if it had happened under his nose, because he never saw anything when he was talking about physics. He had temporarily forgotten his annoyance at the changes to the Institute, and he seemed quite pleased with life.

I wasn’t. I had been brought to the Institute so that McAndrew and I could fly half a light-year from home with Lyle and Parmikan. Anna Griss had engineered my arrival. It was inconceivable that the surprises were all over.

What little goodies were in store when Anna’s bully-boys and I were flying far off in the Hoatzin?

I lost track of that question in the busy days before departure. The Hoatzin was primed and ready, but I hadn’t performed my engine inspection or any of the other preparations that I like to do. I went over the ship, checking everything, and found nothing worse than a slight imbalance in the drive that would have meant a mid-course correction at ship turn-around, a quarter of a light-year from Sol.

Neither Lyle nor Parmikan gave me any trouble. In fact, I hardly saw them until the four of us assembled for final check-in and departure. Then Stefan Parmikan rolled up with about ten times as much baggage as he was allowed.

He objected strongly when I told him to take it away. “All that space.” He pointed outside, to the Hoatzin with its hundred meter mass disk and the four hundred meter axle sticking out like a great grey spike from its center. “There’s oceans of room for my stuff.”

How could a man reach adulthood today, and know so little about the McAndrew balanced drive?

“The disk you’re pointing at is solid compressed matter,” I said. “Density is twelve hundred tons per cubic centimeter, and surface gravity is a hundred and ten gees. If you want to strap your luggage on the outside of that, good luck to you.”

“What about the axle? I can see that it’s hollow.”

“It is. And it has to stay that way, so the living-capsule can move up and down it. Otherwise we couldn’t balance the gravitational and inertial accelerations. Either we move the capsule in closer to the disk as we increase the acceleration, or you tell me how we’re going to survive a hundred gees.” When he still didn’t show much sign of understanding me, I waved my hand. “The total living accommodation of the Hoatzin is that four-meter sphere. I’m not going to spend the next month falling over your stuff. And I’m not going to waste time arguing. That luggage isn’t going with us. That’s final. Get it out of here, so we can prepare to board.”

Parmikan glowered and grumbled, and finally dragged it away. When he reappeared an hour later with a much smaller package I hustled everyone onto the Hoatzin as quickly as possible to avoid any more hold-ups. Maybe I wasn’t as thorough as I should have been inspecting luggage. But I suspect it would have done no good if I had been. There must be a definite threat before you start opening people’s personal effects. I was anticipating rudeness and arguments and possible discipline problems, but not danger.

Let’s call that my second mistake in Project Missing Matter.

Once we were under way I felt a lot better. With the drive on the perimeter of the mass disk turned on, the Hoatzin is surrounded by a sheath of highly relativistic plasma. Signals won’t penetrate it. Communications with Anna Griss, or anyone else back in the Solar System, were blocked. That suited me fine.

By the end of the first twenty-four hours at full drive we were doing well. We were up to a quarter of light-speed, heading out from Sol at right angles to the plane of the ecliptic and already at the distance of Neptune. We had settled into a typical shipboard routine, each person giving the others as much space as possible. You do that when you know you have to spend a long time packed together into a space no bigger than a fair-sized kitchen.

And then, unexpectedly, our communications silence caused trouble.

The Hoatzin had been pleasantly quiet for hours. McAndrew had donned a suit, one of the new transparent models so light that you could sit in high vacuum and hardly realize you had a suit on at all.

He was going outside. Most people would be terrified at the prospect of leaving the capsule when the drive is on — if for any reason it turned off, the capsule would automatically spring out to the far end of the axle, to hold the interior field at one gee. But anyone not firmly secured to the capsule would fall at a hundred gee acceleration towards the mass disk. A quick end, and a messy one.

It never occurred to McAndrew that his inventions might fail. He had happily gone outside, for a status check of one of the new mass detectors that he would be using when we reached our destination in the middle of nowhere. We were heading for the region of lowest matter density known, out beyond the limits of the Oort cloud where we would find less than one atom per hundred cubic meters.

I was looking at the outside display screens, partly to scan the plume of plasma behind the Hoatzin for any sign of drive variability, and partly, to tell the truth, because I wanted to keep my eye on McAndrew. He doesn’t believe the balanced drive can give trouble, despite the fact that its very first use nearly killed him.

While I had my attention on the screens, Stefan Parmikan crept up behind me. I didn’t know he was there until I heard a soft, sibilant voice in my ear. “I am required to send a report to the Council every day, and be able to receive messages from them.”

I jerked around. Parmikan’s face was only a foot from mine. It was probably not his fault, but why was his mouth always so wet-looking?

“But Professor McAndrew tells me that we cannot send messages to Terra when the drive is turned on,” he continued.

“Quite right. To Terra, or anywhere else. The signals can’t get through.”

“In that case, the drive must be turned off once every shipboard day.”

“Forget it.” I was a bit brusque, but Lyle and Parmikan seemed to have come along on the expedition without learning a thing about the ship, the drive, or anything else. And Parmikan didn’t sound like he was asking — he was telling. “We lose a couple of hours every time we turn power on and off,” I went on. “And you’d have the living-capsule going up and down the axle like a yo-yo, to balance the change in acceleration from a hundred gee to zero. And anyway, once we’re a long way out the signal travel time is so long the messages would be useless.”