But now for the mysteries: He had never, in all the many years since first we met, sent a letter to “Captain Roker,” or signed himself with his full name. I was always “Jeanie” when he wrote to me, while he signed as “Mac” or “Macavity” — my private Old Possum-ish name for him, because like Macavity the Mystery Cat, McAndrew did things that seemed to break the law of gravity.

Second, he didn’t write when he was planning an expedition. There would be a random call, at any hour of the day or night. He was thinking of making a trip, he’d say vaguely. Would I perhaps like to go along?

Third — a detail, but one that chafed my ego — I was invited to go on the Project Missing Matter expedition as a crew member. Mac knew that I’d served as ship’s captain, and only as captain, for fifteen years.

Fourth, the whole tone of the letter was too stilted and officious to be genuine McAndrew. He couldn’t sound that formal if he tried.

And one more mystery, to round out the set. Who the devil was Dorian Jarver? I thought I knew all the key scientists at the Penrose Institute.

That question was fifth on the list, and the least important until I tried to call McAndrew for an explanation. Then instead of the old direct-access lines into individual offices at the Penrose Institute, I found myself dumped to a Message Center where my call was at once rerouted from McAndrew to Dorian Jarver. Director Jarver is unavailable, said a polite voice. Please leave your name, and he will return the call as soon as possible.

I hung up without waiting to learn if the voice at the other end was live or recorded. Director Jarver? What had happened to my old friend Professor Limperis, the blackest man alive, who had run the Institute since long before my first visit?

Finding the answer to that was not difficult. I tapped one of the general data bases and queried for the staff file of the Penrose Institute. Professor Limperis was listed, sure enough — but as professor emeritus and ex-Director. The new director was Dr. Dorian Jarver, former head of the Terran science applications group, and — bad sign — nephew of Councilor Griss, head of Terran Food and Energy.

Anna Lisa Griss, that was, a lady whose arm McAndrew had once, with the best of possible intentions, cut off with a power laser out in the Oort cloud. It would have been regrown, long since; but I doubted that the memory had faded with the scar.

I followed an old McAndrew principle, and went to a publications data base. Dorian Jarver was there, with eight or nine decent-sounding physics papers credited to him; but they were not recent. The newest one was eleven years old. The new director of the Penrose Institute appeared to be an ex-physicist.

McAndrew was anything but an ex-physicist. Why would he cite his own name and Jarver’s as someone I might contact?

When I received the message from McAndrew I was on the tail end of a routine run home from Titan. As soon as the Assembly I had been piloting was tucked away and all its Sections placed in a stable parking orbit, I signed off and headed straight for the Penrose Institute aboard one of the 5-gee mini-versions of the McAndrew balanced drive.

“I invite you to contact me or Dr. Dorian Jarver,” the letter had said. Contact can surely include a visit.

The outline of the Institute at last appeared as a lumpy and spiky double-egg during my final approach. I examined it closely. It would wander around the Inner Solar System depending on research needs, anywhere between Mercury and the Belt, but its facilities shouldn’t change. They hadn’t. As we docked I could see the Dotterel and the Merganser moored in the external hoists. They were the first prototypes using the McAndrew balanced drive (which everyone else, to Mac’s intense annoyance, insists on calling the McAndrew inertia-less drive). Those early ships were no longer in use. They had been replaced by a more advanced design, embodied in the Hoatzin. I could see its bulky massplate and longer central spike off in the distance. It appeared slightly grubby and battered-looking, as befitted the first and only ship to visit both the Ark of Massingham and the Oort cloud.

The changes began inside, as soon as I passed through the lock. In the old Institute the visitor found herself wading at once through a junkyard of obsolete equipment waiting for disposal. It would have been quite an obstacle course in an emergency, but nobody had ever seemed worried about that.

Now I found myself in a clean and uncluttered chamber. The walls were painted white, the floor was polished grey, and in the middle of the room sat something that the Institute had surely never seen before: a long desk, two receptionists, and in front of them, a sign-in terminal and a tray of badges.

The woman behind the desk went on fiddling with a great bank of controls in front of her, all flickering lights and low humming, but the man glanced up at me inquiringly.

“I’m here to see McAndrew,” I said, and started towards the corridor on the left. I’d been here scores of times, and I knew where Mac hung out, in a cluttered room that made even the old entry to the Institute look elegant. Mac didn’t throw away junk equipment. He kept it in his office.

“Not that way, ma’am,” said the man politely. “Professor McAndrew is the other way now. You will need an escort. And if you’d first please check in…”

McAndrew’s voice was starting to whisper in my ear. By the time that I had signed in, stated my identity, had my ID independently checked with a DNA mapper, been assigned a badge, and refused refreshments (how long did they expect me to be in the reception area?) Mac’s voice was shouting at me. “Help, Jeanie,” it screamed. “Help, help, help!”

This wasn’t the Penrose Institute that I had known, the place of casual procedure and superb science where Mac had worked for half his life. It had become a clone of a thousand Earthside technology offices.

And it got worse. When I, checked and signed and badged, was led away towards the new working offices, I still did not reach McAndrew. “In a few minutes,” said my guide, in answer to my question. “But first, the Director.”

I was ushered into a new chamber, starkly clean and sparsely furnished. My guide left at once and I looked around. There was no desk, no terminal. Over in one corner on an angular white chair sat an equally angular and thoughtful man, fingertips touching in front of his face.

“Captain Roker,” he said, and stood up. He smiled, very white teeth in a thin-lipped, worried countenance. “I’m Dorian Jarver, the Director of the Penrose Institute. I must say I didn’t expect a visit until you’d heard more about the project. But it’s a blessing that you’re here, because now we can all do our best to persuade you.”

“I’m persuaded already.” I realized that was true, and had been since I saw that ritzy new entrance foyer. “I’m reporting for duty right now.”

“For the expedition described in Professor McAndrew’s letter to you? But the mission and your role in it are not yet fully defined.”

“You can define that later. I’m here, and I’m ready to start.”

Dorian Jarver must have been surprised at both my arrival and my instant acceptance. “I’m delighted to hear that,” he said, though he didn’t sound it. “You come to us with the highest recommendations. And I have to admit that I’ve been a little worried about this proposed expedition. It could be dangerous, and Professor McAndrew is too valuable to risk. He’s one of our most priceless assets.”

No matter what else he didn’t know, he obviously understood McAndrew. It could be dangerous, because Mac would charge into Hell itself if he saw some intriguing scientific fact sitting in the innermost circle. He was too valuable to risk. But Jarver’s final word was disturbing to me. Not a scientist, not a human being. An asset.