Casimir said, "Where did my radioactive source fall to? Are we going anywhere near there?"

"Good point," said Fred Fine. "Let's steer clear of that. Don't want blasted 'nads."

"I know where it went, but it's not there now," said Virgil. "The rats ate everything. Some rat obviously got a free surprise in with his paraffin, but I don't know where he ended up.' Fred Fine began to point out landmarks: where he had left the corpse of the Microwave Lizard, long since eaten by you know what; where Steven Wilson had experienced his last and biggest surprise; the tunnel that led to the Sepulchre of Keldor. His voice alternated between the pseudo-scientific dynamo hum of Fred Fine and the guttural baritone of the war hero. We had heard this stuff from him for a couple of weeks now, but down in the tunnels it really started to perturb us. Most people, on listening to a string of nonsense, will tend to doubt their own sanity before they realize that the person who is jabbering at them is really the one with the damaged brain. That night, tramping through offal, attacking giant rats with a strobe light and listening to the bizarre memoirs of Klystron, most of us were independently wondering whether or not we were crazy. So when we asked Fred Fine for explanations, it was not because we wanted to hear more Klystron stories (as he assumed); it was because we wanted to get an idea of what other people were thinking. We were quickly able to realize that the world was indeed okay, that Fred Fine was bonkers and we were fine.

Hundreds of cracked and gnawed bones littered one intersection, and Virgil identified it as where he had discovered the useful properties of the Sceptre. This area was high and dry, as these things went, and many rats lurked about. Virgil switched the Sceptre on for good, forcing them back to the edge of the dark, where they chattered and flashed their red eyes. Hyacinth stuffed wads of cotton in her ears, apparently in case of a shootout.

"Let's set up the 'scope," Virgil suggested. Casimir swung off his pack and withdrew a heavily padded box, from which he took a small portable oscilloscope. This device had a tiny TV screen which would display sound patterns picked up by a shotgun microphone which was also in the pack. As the 'scope warmed up, Casimir plugged the microphone cord into a socket on its front. A thin luminous green line traced across the middle of the screen.

Virgil aimed the mike down the main passageway and turned it on. The line on the screen split into a chaotic tangle of dim green static. Casimir played with various knobs, and quickly the wild flailing of the signal was compressed into a pattern of random vibes scrambling across the screen. "White noise," said Fred Fine. "Static to you laymen."

"Keep an eye on it," said Virgil, and pointed the mike down the smaller side tunnel. The white noise was abruptly replaced by nearly vertical lines marching across the screen. Casimir compressed the signal down again, and we saw that it was nothing more than a single stationary sine wave, slightly unruly but basically stable.

"Very interesting," said Fred Fine.

"What's going on?" Sarah asked.

"This is a continuous ultrasonic tone," said Virgil. "It's like an unceasing dog whistle. It comes from some artificial source down that tunnel. You see, when I point the mike in most directions we get white noise, which is normal. But this is a loud sound at a single pitch. To the rats it would sound like a drawn-out note on an organ. That explains why they cluster in this particular area; it's music to their ears, though it's very simple music. In fact, it's monotonous."

"How did you know to look for this?" asked Sarah.

Virgil shrugged. "It was plausible that an installation as modern and carefully guarded as the one I saw would have some kind of ultrasonic alarm system. It's pretty standard."

"Very interesting," said Fred Fine.

"It's like sonar. Anything that disturbs the echo, within a certain range, sets off the alarm. Here's the question: why don't the rats set it off?"

"Some kind of barrier keeps them away," said Casimir.

"I agree. But I didn't see any barrier. When I was here before, they could run right up to the door– they had to be fought off with machine guns. They must have put up a barrier since I was last down here. What that means to us is this: we can go as far as the barrier, whatever it may be, without any fear of setting off the alarm system."

We moved down the tunnel in a flying wedge, making use of table leg, Sceptre and sword as necessary. Soon we arrived at the barrier, which turned out to be insubstantial but difficult to miss: a frame of angle-irons welded together along the walls and ceiling, hung with dozens of small, brilliant spotlights. At this point, any rat would find itself bathed in blinding light and turn back in terror and pain. Beyond this wall of light there was only a single line of footprints– human– in the bat guano. "Someone's been changing the light bulbs," concluded Sarah.

The fifty feet of corridor preceding the light-wall were littered almost knee-deep in glittering scraps of tinfoil and other bright objects, including the remains of Fred Fine's radio. "This is their hangout," said Hyacinth. "They must like the music."

"They want to make a nice, juicy meal out of whoever changes those light bulbs," suggested Fred Fine.

Sarah's pack contained a tripod and a pair of fine binoculars. Once we had set these up in the middle of the tunnel we could see the heavy doors, TV cameras, lights and so on at the tunnel's end. As we took turns looking and speculating, Virgil set up a Geiger counter from Sarah's pack.

"Normally a Geiger counter would just pick up a lot of background and cosmic radiation and anything meaningful would be drowned out. But we're so well shielded in these tunnels that the only thing getting to us should be a few very powerful cosmic rays, and neutrinos, which this won't pick up anyway." The Geiger counter began to click, perhaps once every four seconds.

Sarah had the best eyes; she sat crosslegged on the layers of foil and gazed into the binoculars. "In a few minutes a hazardous waste pickup is scheduled for the loading dock upstairs," said Virgil, checking his watch. "My theory is that, in addition to taking hazardous wastes out of the Plex, those trucks have been bringing something even more hazardous into the Plex, and down into this tunnel."

We waited.

"Okay," said Sarah, "Elevator door opening on the right." We all heard it.

"Long metal cylinder thingie on a cart. Now the end of the tunnel is opening up– big doors, like jaws. Now some guys in yellow are rolling the cylinder into a large room back there." The Geiger counter shouted. I looked at Casimir.

"Skip your next chest X-ray," he said. "If this place is what it looks like, it's just Iodine-131. Half-life of eight days. It'll end up in your thyroid, which you don't really need anyway."

"I'm pretty fond of my thyroid," said Hyacinth. "It made me big and strong."

"Doors closing," said Sarah over the chatter of us and the Geiger counter. "Elevator's gone. All doors closed now." "Well! Congratulations, Virgil," said Fred Fine, shaking his hand. "You've discovered the only permanent high-level radioactive waste disposal facility in the United States."

Most of us didn't have anything to say about it. We mainly wanted to get back home.

"Fascinating, brilliant," continued Fred Fine, as we headed back. "In today's competitive higher education market, there has to be some way for universities to support themselves. What better way than to enter lucrative high-technology sectors?"

"Don't have to grovel for the alumni anymore," said Sarah. "You really think universities should be garbage dumps for the worst by-products of civilization?" asked Hyacinth.

"It's not such a bad idea, in a way," said Casimir. "Better the universities than anyone else. Oxford, Heidelberg, Paris, all those places have lasted for centuries longer than any government. Only the Church has lasted longer, and the Vatican doesn't need the money."