She went quietly across to the outer door and opened it. She knocked and called, “Anyone here? May I come in?”

How bogus could you get? But he was answering, “I’m through here. Just a minute.”

It was more like twenty seconds before he appeared in slacks and a short-sleeved shirt. His hair still fell damp over his forehead, and he was barefoot.

“We were supposed to have a meeting this morning.” Maddy tried to look him in the eye, and failed. “You weren’t where I thought you would be. So I tried here. I guess you forgot we had a meeting.”

“No.” He smiled at her. “I’d never forget a meeting with you.”

Something about him had changed. Maddy had an idea what. As long as the crisis lasted he would be the focus for all the engineering work on Sky City, and he drew power from that. Just as she felt more and more useless, he was increasingly in control.

He went on, “I came here because I’d been up all night. I wanted to look my best when I met you, and I thought a shower and a change of clothes would do the trick. It did the trick, all right. The last thing I remember is sitting down in the bathroom to dry myself off. Then I was on my bed, staring at the ceiling. You know all about the particle burst?”

“The blip storm? That’s what they’re calling it. Yes, nobody’s talking of anything else.”

“Then you know I don’t have much time to talk. What’s on your mind?”

Did he realize who had moved him from the bathroom? Had he seen her standing at the foot of the bed, inspecting him?

No time to worry about that. John had his shoes on, and he was already leading them out of his quarters.

Maddy said, “It’s about the Sky City murders. That’s what I wanted to talk to you about.”

That stopped him. The corners of his mouth turned down, and he looked ten years older. “What about them?”

“Seth Parsigian and I know who did it. But we don’t have hard evidence, so we need to set up a trap. It would work like this.”

Maddy kept the story short and simple. At the end John seemed older than ever.

“You don’t believe me?” she asked.

“The hell of it is, I do. But I hardly have a spare moment, and it’s going to get worse. I can’t see any way to help.”

“We don’t need help. We just want you to make an announcement.”

“What about Doris Wu’s family? They’ll want details.”

“They’ll not hear of it. Only a few people will. Before word spreads, we’ll have the murderer.”

He hesitated. For the first time, Maddy thought she had a chance.

“When do you want me to announce it?”

“Not now. And not during the blip storm — we’re not ready. The best time will be when the main wave hits.”

“Maddy, that’s the worst possible time. Everything and everyone will be stressed to their limit. This place will be in chaos.”

“Chaos is what the murderer will rely on.” They were approaching the open doors of the information center, and Maddy’s last opportunity for a private discussion. She took John’s arm, so that he had to turn and face her. “We’ll probably only have one chance — ever. The evidence just isn’t there. Will you do it?”

He nodded. “When I first heard about the murders I was upset because I could do nothing. Now maybe I can. Just tell me when. All right?”

Maddy wanted to shout, Yes! She also wanted to hug him. She had no time for either, because the entrance to the information center was suddenly full of people. At the front were Amanda Corrigan and Wilmer Oldfield. Behind them, crowding forward, were Star Vjansander and Lauren Stansfield and two data analysts whose names Maddy didn’t remember.

Star and both data analysts all began to speak at once. But it was Wilmer’s voice, calm and slow and serious, that continued and cut through the rest.

“Amanda found another anomaly in the Sniffer data. If Star’s right in her interpretation, everything just got a lot more interesting. You need to hear about this.”

28

As soon as John was settled in front of the displays, Wilmer Oldfield turned to Amanda Corrigan. “Ready to begin? It’s your discovery.”

“But I had no idea what I’d found.” Amanda wriggled in embarrassment and looked at the audience. Seven people, including Maddy hovering at the back. That was too many for Amanda’s comfort. She turned back to Wilmer Oldfield. “You explained it to me. Can’t you talk about it?”

“I’ll do the first bit, then we’ll see.” Wilmer moved to the display control panel and glanced at John. “Ask questions anytime, because I don’t know the best place to start. Let’s go with the first Sniffers we sent out, and what they measured. They were high-acceleration probes with low-cross-section instruments.” He moved the pen across the control pad, and a thin, wobbly line with a distinct curve appeared on the display.

Wilmer stared at it with disgust. “These bloody gadgets. Isn’t there a board someplace that I can draw on?”

“Behind you.” Lauren Stansfield stepped over to a wall and opened two small doors to reveal a white board. Maddy noticed that Lauren alone, of all the people in the room, was wearing custom-made clothing. The pin on her left breast glowed with the varying colors of a fire opal. Expensive — even if no one else in the room but Maddy knew it.

“Write with this,” Lauren went on. “Erase with this pad — a touch is enough, the pen is electronic.”

“Right.” Wilmer drew a small circle. “Here we are. And here’s Alpha C.” Another small circle. “And here’s the path of a Sniffer.”

He drew a wavering line between the two stellar systems. To Maddy’s eye it was no better than his effort at the control panel, but Wilmer nodded at it in satisfaction.

“Good enough. Now let’s look at the particles flung out by the Alpha C supernova. If you didn’t know any better, you’d expect them to spread out pretty much equally in all directions. Spheres, like this, expanding in time.”

He drew a set of rough circles, each centered on the point that depicted Alpha Centauri.

“If that’s what was happening, the particle density would go down as the inverse square of the distance from the supernova, as the surface area they pass through goes up. Then the number of particles that a Sniffer measured would be less for the Sniffers that were launched later, simply because they meet the particle flux farther from Alpha C.

“But we know that the particles and radiation didn’t come out equally in all directions — the gamma pulse proved that twenty-seven years ago. Instead, a shell of gases around the supernova bottled up everything inside. That shell expanded and thinned, until finally it was weak enough to rupture. Then everything — gamma rays and particles — could squirt out from inside in one particular direction. Like this.”

Wilmer erased the set of spheres and replaced them with a narrow cone, its point on Alpha Centauri and its axis running toward the solar system.

“Think of it like a searchlight beam. No matter how tightly focused the beam is, as you go farther away from the searchlight the circle of light that it throws gets bigger, and the brightness of the light in that circle becomes less. With lasers, the spread can be very small, so sometimes it looks like the beam’s not spreading at all. Sort of like this.”

He replaced the cone by a long, narrow cylinder, running between Alpha Centauri and Sol.

“That looks like the worst case imaginable.” Wilmer laid down the marker. “For it to happen, the particles thrown out by Alpha C would have to come straight at Sol, with no beam spreading at all. Looked impossible, so we didn’t worry about that case. The most reasonable situation seemed like the second one, the particles lying in a narrow cone that gradually widened as they went farther from Alpha C. And that’s exactly what the first Sniffers found. Sniffer-B met the particle wave farther away from the supernova, and the particle counts that it measured were less than for Sniffer-A. The density was falling like the inverse square of the distance. No worries.