“A satisfactory interpretation. Good luck.”

“Thanks. And you will keep the other and most pressing matter of a certain injection on the top of your agenda?”

“I shall query the people involved hourly on the hour,” he said grimly-and I think he meant it.

We filled our packs, kept the good-bys as brief as possible, loaded up and followed Fido out without a backward glance. I liked Madonette. Perhaps too much while I was on an assignment like this. Go, Jim, go I cozened. Follow your wandering tachyon.

We followed the flapping black nylon tail through the streets and onward to the outlying farms. The women we met waved happily, some even whistling bits of our tunes to cheer us on the way. The last farm fell behind us and the open plains opened out ahead. I clacked my jaw-radio.

“Are you there, Tremearne?”

“Listening in.”

“Any tribes of nomads around-or up ahead?”

“Negative.”

“Any buildings, farms, people, sheots – anything visible on this heading?”

“Negative. We’ve done a detailed scan as far north as the polar ace. Nothing.”

“Thanks. Over and out.” Wonderful.

“Empty on all sides, nothing at all ahead,” I reported to Floyd. “So we just stay on this heading until our plastic retriever detects any tachyons-or we reach the north pole and freeze to death.”

“I’ve been meaning to ask. What’s a tachyon?”

“Good question. Up until now I thought it was just a theoretical unit that the physicists dreamed up in order to explain how the universe works. One of the subatomic entities that exist either as waves or particles. Until they are observed they have no real existence. It has been said, and who am I to doubt it, that they exist in a probabilities limbo of many possible superimposed states.” I noticed that Floyd’s jaw was beginning to drop, his eyes to glaze. He shook his head.

“You are going to have to try harder, Jim – you lost me a long time back.”

“Right, sorry. Try this. There are various kinds of units in physics. A photon is a unit of light energy and an electron is a unit of electric energy. Okay?”

“Great. With you so far.”

“A graviton is a unit of gravity and a tachyon a unit of time.”

“Lost me again. I thought minutes and seconds were units of time?”

“They are, Floyd, but just to simple people like you and I. Physicists tend to look at things in a different manner.”

“I believe it. Sorry I asked. Time for a break, five minutes in every hour.”

“You’re on.” I unstuck my canteen and took a swig, then whistled to our dogtrotting terminal that was almost out of sight. “Come back Fido, breakies.”

“You’re the boss,” Aida said. The dog scrambled back, barked and sniffed my pack where I had dropped it next to me on the ground.

“Not too much realism!” I shouted. “Don’t have that plastic canine lift its leg on my pack!”

The day went on like that. Apparently forever. We crawled across the landscape: the sun crawled across the sky. When w e had been walking for over five hours fatigue began to strike. Floyd was striding ahead at a great pace.

“Tired yet?” I called out.

“No. Great fun.”

“To those of us who weren’t bashed about by the red peril.”

“Just a bit more.”

The bit more went on a bit more than I appreciated and I was just about to toss in the towel when Fido spoke.

“Bow and wow, gentlemen. Just detected a couple of tachyons as they went whizzing by. Wasn’t sure of the first one but-there it is, another – and another!”

“Coming from where?” I asked.

“Directly ahead. Let’s just stay on this course and we’ll track the source down. With, perhaps, yes I’m sure, there is the strong possibility of a course deviation later.”

“Aha!” I aha’ed. “I recognize equivocation when I hear it. Even from a plastic dog mouthpiece for an ancient ship’s computer.”

“The word ancient is so hurtful…”

“I’ll apologize when you tell me about this complication.”

“Apology accepted. Allowing for the curvature of the planet, gravitic anomalies and other factors, I am still forced to believe that the tachyon source is not on the surface of this world.”

“The thing is underground?”

“Underground is the very word for it.”

I bit hard on the jawphone. “Tremearne, would you put the admiral on the line.”

“I’m here, Jim. Aida reported this possibility a while back and 1 have been . monitoring developments since then. Didn’t want to bother you, for all the obvious reasons.”

“Yes, like we forgot to bring a shovel. Anything else you haven’t told me?”

“I was waiting for data, Just coming in. I sent a low flying probe to look for the gravimetric anomalies that Aida had found. Looks like there are a number of them and they are being plotted now.”

“What kind of anomalies? Metal deposits?”

“Quite the opposite. Caverns below the ground.”

“It figures. Over and out. At least we now know where the artifact is.”

“Where?” Floyd asked, since he had only heard my side of the conversation.

“Underground. There are caves or caverns of some kind up ahead. Nothing visible on the surface-but they are there all right. Our technical observers seem sure that the artifact is down there somewhere. Can we take that break now and wait for the reports?”

“I guess so.”

Floyd guessed right, which was a good thing since an instant after we dropped to the ground the stream of bullets was fired at us. Zipping through the empty air where we had just been standing.

Floyd had a large and ugly pistol in his hand now which didn’t slow him down as he wriggled on hands and knees beside me to the shelter of the mounded earth around a polpettone tree.

“We’re under fire!” I shouted into my jawphone.

“Source not visible.”

Fido stood on its hind legs-then jumped high into the air despite another burst of bullets.

“Bow-wow. Perhaps not visible to others but clear enough to me.”

“What is it?”

“Some sort of apparatus at ground level. Want me to take it out?”

“If you can.”

“Grrr!” it growled and retracted its legs, then zipped off at a great rate at ground level, so fast it could barely be seen. Moments later there was a muffled explosion and bits of debris rattled dorm into the shrub.

“’That was quick,” I said.

“Thank you,” Fido said emerging from the undergrowth with a jagged bit of metal in its jaws. “Just follow me if you want to see the remains.”

We followed the thing to a smoking pit with a jumble of crumpled apparatus in its center. Fido dropped its bit of debris, lifted one front leg. Extended its head, straightened its tail and pointed.

“Remote controlled gun turret. Note that the top of it is camouflaged, concealed by dirt and sprouting plants. Hydraulically operated-that’s red oil not blood-to lift the apparatus above ground level. Remains of an optical finder there. Note the four automatic guns, Rapellit-binetti X-nineteens. Rate of fire twelve hundred rounds a minute. Eighty rounds a second, explosive and armor piercing.”

“Since when have you been an armament authority, Aida?” I asked.

“Since a long time back, -sweetie-pie. In my heyday I was required to know this sort of thing. I also know that these particular guns have not been manufactured for over five hundred years.”