The joke, such as it was, would have been completely unacceptable when uttered in public, or even in a meeting, and so this was a way of saying to Doob, You are in my confidence. Doob wasn’t a leader, but he was fascinated by people who were, and how they went about their work.

“Ivy’s figuring out the ramifications of not having those arklets, those supplies.”

“Thank God for Ivy,” Markus said. Since winning command of the Cloud Ark he had never lost an opportunity to praise her—another skill that Doob reckoned must be inculcated into leaders in whatever mysterious Leader Academy churned them out. More likely it was an instinct.

“Well, my day begins,” Markus continued. “Thank you for the briefing.” Markus, like a lot of the Europeans, ran on third shift, which meant that he was, in fact, beginning his day a couple of hours early.

“Mine is winding down,” Doob said. “I thought I would get drunk with some miners.”

“No better people for it,” Markus said with a wink. “I believe Dinah will be out in a minute. I think she would enjoy seeing you.”

With that Markus pulled his phone from the pocket of his coverall and turned his attention to its screen while using the other hand to pull himself out of this module and down the Stack.

Doob was left floating in the middle of the SCRUM. The only thing between him and Dinah was a privacy curtain. He was about to say “Knock knock!” when he heard a string of beeps emerge from a speaker on the other side. An incoming Morse code transmission, which he had not the skill to understand. To that point Dinah had been quiescent, but he now heard her going into movement, peeling herself out of her sleeping bag. He thought better of bothering her just now, and decided to check his own email.

SHE RAN ON FIRST SHIFT, WHICH MEANT THAT THIS WAS MIDAFTERNOON for her: traditionally a time when she began to feel a little drowsy even when Markus had not just been helping her relax. She felt that going fully to sleep would be a bad idea, partly because she had work to do and partly because it would lead to more gossip than was happening already. She could hear Markus chitchatting with Dubois Harris on the other side of the curtain. She knew that he was stalling for her, giving her some time to pull herself together; she was duly appreciative, and she made the most of it, gliding in the liminal zone between dozing and waking until her radio began to beep. She knew immediately that this was not Rufus; she could tell as much by the “fist” of the transmission. It was faint and it was clearly not the work of an experienced ham.

Her eyes opened as a thought came to her: maybe this was the source known as the Space Troll. That term had originated with Rufus, who had first mentioned it several days ago: Have you heard from the Space Troll yet? It was his name for a transmitter that he had begun picking up recently, and it matched what Dinah was hearing now.

She ejected herself from the bag, turned up the volume on the receiver, and listened while pulling on a T-shirt and some drawstring pants. The signal sounded as if it was coming in from a home-brew transmitter. The owner had a sketchy understanding of the practices and etiquette of the CW (Morse code–using) radio world. His dots and dashes were perfectly formed, and came rapidly, as much as proving that he was using a computer keyboard and an app that automatically converted keystrokes into Morse. He was sending out a lot of QRKs and QRNs, which were queries about the strength of his own signal and the degree to which it was being interfered with. So, he seemed a little insecure about the quality of his equipment.

According to Rufus, as soon as you started transmitting back to the Space Troll he would shoot back a spate of QRSes, meaning “please transmit more slowly,” further proof that he was a novice using a computer keyboard to form the groups, but not very good at deciphering what came back. He transmitted on one frequency only, which was the one that Rufus had, until a year ago, generally used to contact Dinah. This had become known to the Internet in the wake of a human interest story about the MacQuarie family, and so for a few weeks it had been damned near unusable as every CW ham on the planet had tried to use it to contact Dinah. Then word had gotten around that the MacQuaries père et fille weren’t using it anymore and it had gone pretty silent, except for a few people who apparently hadn’t gotten the memo, such as the Space Troll. Anyway, Rufus had gone back to monitoring that frequency again and Dinah was now doing likewise. She had not personally heard any transmissions from the Space Troll. This was not remarkable. Her antenna was nothing compared to the one that Rufus had installed above his mine, and her receiver was something out of a fifth-grade science project. Except when Izzy was passing over his meridian, she and Rufus would naturally “hear” different stations.

According to Rufus, having a conversation with the Space Troll required patience or a sense of humor. The fact that novice hams were screwing around on the radio, which would have driven Rufus into a spasm of righteous fury a few years ago, now just seemed like a sign of the times. Of course people were getting interested in amateur radio; the Internet was expected to go down as soon as the Hard Rain started. And of course many of them were novices.

When they finally did begin an intelligible conversation, Rufus would send QTH, which meant “where are you?” and would get back QET. This was an unofficial Q code, a sort of corny joke meaning “not on planet Earth.”

And that was why Rufus called this guy the Space Troll. Because, among other oddities, he didn’t have a call sign, or at least didn’t use one. The signal she was hearing now was QRA QET, repeated every few seconds; it meant, basically, “Hello, this is E.T., is anyone listening?”

Dinah generally kept the transmit side of her rig turned off when not in use. She turned it on now, but kept her hand well clear of the brass telegraph key. Lurking and listening were harmless, but as soon as she touched that thing, the Space Troll would hear an answering beep, and then she might never be rid of him. More likely, though, was that the Space Troll would give up after a while. Then she could transmit to Rufus, who’d be coming up over the horizon in a few minutes, and let him know that she too had heard from the mysterious “extraterrestrial.” It would be good for a laugh, and a few minutes’ distraction. Her father sounded like he could use some of both.

It had long since become obvious that he and a number of his mining industry friends had mounted a serious operation to prepare for an extended stay beneath the surface of the Earth. They were hardly the only ones to think that way; people were digging holes in the ground all over the world. Most of them would be dead within hours or days of the beginning of the Hard Rain. Constructing an underground complex that could sustain itself for thousands of years was an operation of which few, if any, organizations were capable. Most of those were governmental or military. But if any private group could do it, it was Rufus and his network. The sorts of questions he had been asking her for the last two years left nothing to the imagination. To the extent that the experts on Izzy knew anything about long-term sustainability of artificial ecosystems, Rufus now knew it too.

Distracted by thinking about Rufus and his mine, Dinah became aware that the Space Troll’s transmission had changed. Instead of the familiar QRA QET, it now began with QSO, which in this context meant “can you communicate with . . . ?” This was followed by an unfamiliar call sign, which she didn’t recognize as such because it was so long: a string of digits and letters that didn’t follow any of the standard conventions for radio call signs.