The Domino Pattern

The occupants of those seats, not surprisingly, had found somewhere else to be for the moment.

“We couldn’t bring in a couple of cameras so the whole train could watch?” I grumbled as we passed our third knot of rubberneckers.

“I thought you’d want to take the sample yourself,” Bayta countered, a slight edge to her voice. Clearly, she didn’t like having the Quadrail’s innards exposed to the paying customers this way any more than I did, and she didn’t appreciate me getting on her case about it. “There’s no way you could have reached the filter while it was still in place.”

And given the tight tolerances of Quadrail floor space, there was probably nowhere more private where they could have lugged the filter assembly for the procedure. “I suppose,” I conceded.

We reached the hanging plate, and I took a moment to study its upper side. The filter assembly consisted of about a dozen boxes of various sizes and shapes scattered across the plate, all of them marked with incomprehensible dot codes. They were connected to each other by a bewildering and colorful spaghetti of tubes, ducts, cables, and wires. Other tubes and conduits, carefully sealed off, ran to the edges of the plate, where presumably they connected to equipment tucked away above the rest of the ceiling. The plate itself had sixteen connectors, four per side, for fastening it to the rest of the ceiling. The connectors, I noted, were accessible only from above. It was pretty clear that no one was going to tamper with the system without Spider help. “Which one do I want?” I asked Bayta.

“That one,” she said, pointing to the largest of the boxes. “The Spiders will take off the cover for you.”

“Thanks,” I said, looking down at the mites grouped around us like shiny seven-legged lap dogs. “Do they need a boost?”

“No,” Bayta said, and I quickly stepped back as a pair of fist-sized twitters appeared from inside the ceiling and deftly slid down the corner lines onto the exposed machinery. Picking their way across the miniature landscape, they reached the box Bayta had indicated and started removing one of its sides.

“Here,” Bayta said, pressing a pair of sample vials into my hand. “Will you need a hypo or scraper?”

“Got one, thanks,” I said, pulling out my multitool and selecting one of the blades. The twitters got the filter’s side off, and I leaned in for a closer look.

I’d expected to find some sort of thin but tangible layer of fluffiness, the sort of thing you might find in an office building air filter that hadn’t been replaced for a few weeks. But the dimpled white material sitting in front of me looked as clean and fresh as if it had come right out of the box.

It looked, in fact, like some industrious Spider had given it a thorough cleaning sometime in the past few hours. And if one of them had, this whole thing was going to be a complete waste of time. “You did warn the Spiders not to clean it, didn’t you?”

“Of course,” Bayta said. “It hasn’t been touched since Homshil.”

“Looks pretty clean to me,” I pointed out.

“It’s the third-stage filter,” she said. “It always looks clean.”

I suppressed a grimace. Of course it did. All the larger dust and lint particles would have been captured by a larger-mesh filter somewhere upstream in the system. But it was this filter that would have a shot at trapping impurities the size of cadmium atoms and compounds. “Just making sure,” I said, trying to salvage a little dignity.

Experimentally, I gently scraped the multitool blade along one edge of the filter. A small cascade of fine white powder appeared and drifted slowly downward. Moving the blade to a different part of the filter. I held one of the vials in position and scraped more of the white powder into it. I waited until the dust had settled and then handed the vial to Bayta for sealing. I repeated the operation on a third section of the filter, again handing the vial to Bayta when I was done. “That should do it.” I told her. Folding the blade back into the multitool, I turned around.

And stopped short. Standing three meters away, right in the center of the ring of gawkers, was the Filly I’d had the brief tussle with earlier that day in the third-class bar. He was Staring at me with an intensity I didn’t at all care for. “Can I help you?” I asked.

“What do you do here?” the Filly asked, his long nose pointing toward the filter assembly.

“Just a routine maintenance sampling,” I said in my best authoritative-but-soothing voice. “Nothing you need to be concerned about.”

I’d used that voice to good advantage many times over the years. Unfortunately, this particular Filly wasn’t buying it. “Is there danger in the air?” he demanded. “Is there risk to us all?”

“There’s no risk to anyone,” I said firmly if not entirely truthfully. “As I said, this is just a routine maintenance check.”

But it was no use. A low-level murmur was already rippling through the rest of the onlookers, some of whom had probably ridden this line before and knew that there was nothing routine about what we were doing. “If there is risk, we deserve to know the truth,” the Filly said firmly, his volume rising to a level that would reach most of the car instead of just the group assembled here at the rear.

“There is no risk,” I said again, letting my gaze drift over the crowd as I tried to think up an answer that would satisfy them. “But you’re right, you deserve to know the truth. If you’ll all be quiet a moment?”

I stopped, waiting for them to pick up on the cue. I could feel Bayta’s eyes on me, and her concern as she wondered what exactly I was doing.

I wondered what I was doing, too. Telling them there was a murderer aboard the train was definitely out—we could wind up with a riot on our hands, with nowhere anyone could escape to. But I’d had enough experience with rumor mills to know that if we didn’t give them something the situation would only get worse, possibly leading to the same riot I was hoping so hard to avoid.

Ergo, I had to give them some truth. The trick, as always, would be to figure out how much.

Slowly, in bits and pieces, the mutterings faded away. “Thank you,” I said. “I presume you’re all aware that two of your fellow travelers died yesterday.”

The last mutterings abruptly vanished. I had their full attention now. all right. I heard Bayta mutter something under her breath, but it wasn’t like the rest of the passengers wouldn’t have noticed the two newly empty seats. “What I’m doing here is checking for the presence of what are called after-elements,” I went on. “Those are bits of nucleic acid residue, antibodies, mucousids—the sorts of things that might have been exhaled by a person in his last battle against a lethal congenital defect.”

The Filly’s nose blaze darkened a bit. “A congenital defect? In both victims?”

“I can see no other likely conclusion,” I said, noting in passing his unusual use of the word victims. “No one else in the car has shown any signs of illness, which eliminates the possibility that they died from some contagious disease.”

I gestured toward a pair of Shorshians near the rear of the crowd. “It can’t even be something specific to Shorshians, since other Shorshians in the car haven’t been affected.”

“So you say it was a congenital disease,” the Filly said, his tone a hit odd.

“As I said, there’s no other likely conclusion.” I repeated. “Nothing for any of you to be concerned about. So please, return to your seats and try to put these unfortunate events from your minds.”

A fresh set of mutterings began to circulate through the onlookers. But the tone was definitely calmer, and at the rear of the group the passengers began obediently heading back toward their seats. Within a minute, the whole crowd had joined the mass migration.

Everyone, that is, except the Filly whose questions had gotten everyone riled up in the first place. He stayed right where he was, his eyes never leaving my face, as the rest of the passengers dispersed. “Was there something else?” I asked.

He took a step closer to me. “You are lying,” he said quietly. “If you sought a congenital disease, a proper investigation would begin with samples taken from the bodies of the victims.”

“I’d like nothing better,” I said. “But there are questions of religious protocol, and the leader of their group has prohibited me from taking direct samples.”

The Filly looked at Bayta, his blaze darkening a little more. “Perhaps that prohibition will yet be lifted,” he said.

“Perhaps,” I said.

He took another step toward me. “But should you discover a different cause of death.” he went on, lowering his voice still more, “I would urge you to let me know at once.”

“In such an unlikely event, I’m sure the Spiders will let everyone know at the same time,” I assured him.