"Actually it's not an ordinary construct," the technician said, glancing over his own report, as if he had already forgotten it; his tone, like the report itself, was dry, dull. This for him was obviously routine.

He, too, agreed that the pinball machine salvaged by the humanoid robots was worthless -- or so Tinbane guessed. "By that I mean it's not like any they've brought to Terra in the past. You can probably get more of an idea directly from the thing; I suggest you put a quarter in it and play through a game." He added, "The lab budget will provide you with a quarter which we'll retrieve from the machine later."

"I've got my own quarter," Tinbane said irritably. He followed the technician through the large, overworked lab, past the elaborate -- and in many cases obsolete -- assortment of analytical devices and partly broken-apart constructs to the work area in the rear.

There, cleaned up, the damage done to it now repaired, stood the pinball machine which the robots had protected. Tinbane inserted a coin; five metal balls at once spilled into the reservoir, and the board at the far end of the machine lit up in a variety of shifting colors.

"Before you shoot the first ball," the technician said to him, standing beside him so that he, too, could watch, "I advise you to take a careful look at the terrain of the machine, the components among which the ball will pass. The horizontal area beneath the protective glass is somewhat interesting. A miniature village, complete with houses, lighted streets, major public buildings, overhead sprintship runnels. . . not a Terran village, of course. An Ionian village, of the sort they're used to. The detail work is superb."

Bending, Tinbane peered. The technician was right; the detail work on the scale-model structures astounded him.

"Tests that measure wear on the moving parts of this machine," the technician informed him, "indicate that it saw a great deal of use. There is considerable tolerance. We estimate that before another thousand games could be completed, the machine would have to go the shop.Their shop, back on Io.

Which is where we understand they build and maintain equipment of this variety." He explained, "By that I mean gambling layouts in general."

"What's the object of the game?" Tinbane asked.

"We have here," the technician explained, "what we call a full-shift set variable. In other words, the terrain through which the steel ball moves is never the same. The number of possible combinations is --" he leafed through his report but was unable to find the exact figure -- "anyhow, quite great. In the millions. It's excessively intricate, in our opinion. Anyhow, if you'll release the first ball you'll see."

Depressing the plunger, Tinbane allowed the first ball to roll from the reservoir and against the impulse-shaft. He then drew back the springloaded shaft and snapped it into release. The ball shot up the channel and bounced free, against a pressure-cushion which imparted swift additional velocity to it.

The ball now dribbled in descent, toward the upper perimeter of the village.

"The initial defense line," the technician said from behind him, "which protects the village proper, is a series of mounds colored, shaped and surfaced to resemble the Ionian landscape. The fidelity is quite obviously painstaking. Probably made from satellites in orbit around Io. You can easily imagine you're seeing an actual piece of that moon from a distance of ten or more miles up."

The steel ball encountered the perimeter of rough terrain. Its trajectory altered, and the ball wobbled uncertainly, no longer going in any particular direction.

"Deflected," Tinbane said, noting how satisfactorily the contours of the terrain acted to deprive the ball of its descending forward motion. "It's going to bypass the village entirely."

The ball, with severely decreased momentum, wandered into a side crease, followed the crease listlessly, and then, just as it appeared to be drifting into the lower take-up slot, abruptly hurtled from a pressure-cushion and back into play.

On the illuminated background a score registered. Victory, of a momentary sort, for the player.

The ball once again menaced the village. Once again it dribbled through the rough terrain, following virtually the same path as before.

"Now you'll notice something moderately important," the technician said. "As it heads toward that same pressure-cushion which it just now hit. Don't watch the ball; watch the cushion."

Tinbane watched. And saw, from the cushion, a tiny wisp of gray smoke. He turned inquiringly toward the technician.

"Now watch the ball!" the technician said sharply.

Again the ball struck the pressure-cushion mounted slightly before the lower take-up slot. This time, however, the cushion failed to react to the ball's impact.

Tinbane blinked as the ball rolled harmlessly on, into the take-up slot and out of play.

"Nothing happened," he said presently.

"That smoke that you saw. Emerging from the wiring of the cushion. An electrical short. Because a rebound from that spot placed the ball in a menacing position -- menacing to the village."

"In other words," Tinbane said, "something took note of the effect the cushion was having on the ball. The assembly operates so as to protect itself from the ball's activity." He had seen this before, in other outspacer gambling gear: sophisticated circuitry which kept the gameboard constantly shifting in such a way as to seem alive -- in such a way as to reduce the chances of the player winning. On this particular construct the player obtained a winning score by inducing the five steel balls to pass into the central layout: the replica of the Ionian hamlet. Hence the hamlet had to be protected. Hence this particular strategically located pressure-cushion required elimination. At least for the time being. Until the overall configurations of topography altered decidedly.

"Nothing new there," the technician said. "You've seen it a dozen times before; I've seen it a hundred times before. Let's say that this pinball machine has seen ten thousand separate games, and each time there's been a careful readjustment of the circuitry directed toward rendering the steel balls neutralized. Let's say that the alterations are cumulative. So by now any given player's score is probably no more than a fraction of early scores, before the circuits had a chance to react. The direction of alteration -- as in all out-spacer gambling mechanisms -- has a zero win factor as the limit toward which it's moving. Justtry to hit the village, Tinbane. We set up a constantly repeating mechanical ball-release and played one hundred and forty games. At no time did a ball ever get near enough to do the village any harm. We kept a record of the scores obtained. A slight but significant drop was registered each time."

He grinned.

"So?" Tinbane said,.

"So nothing. As I told you and as my report says." The technician paused, then. "Except for one thing. Look at this."

Bending, he traced his thin finger across the protective glass of the layout, toward a construct near the center of the replica village. "A photographic record shows that with each game that particular component becomes more articulated. It's being erected by circuitry underneath -- obviously. As is every other change. But this configuration -- doesn't it remind you of something?"

"Looks like a Roman catapult," Tinbane said. "But with a vertical rather than a horizontal axis."

"That's our reaction, too. And look at the sling. In terms of the scale of the village it's inordinately large. Immense, in fact; specifically,it's not to scale ."

"It looks as if it would almost hold --"

"Not almost," the technician said. "We measured it. The size of the sling is exact; one of those steel balls would fit perfectly into it."

"And then?" Tinbane said, feeling chill.

"And then it would hurl the ball back at the player," the lab technician said calmly. "It's aimed directly toward the front of the machine, front and upward." He added, "And it's been virtually completed."

The best defense, Tinbane thought to himself as he studied the out-spacers' illegal pinball machine, is offense. But whoever heard of it in this context?

Zero, he realized, isn't a low enough score to suit the defensive circuitry of the thing. Zero won't do. It's got to strive for less than zero. Why? Because, he decided, it's not really moving toward zero as a limit; it's moving, instead, toward the best defensive pattern. It's too well designed. Or is it?

"You think," he asked the lean, tall lab technician, "that the outspacers intended this?"

"That doesn't matter. At least not from the immediate stand-point. What matters is two factors: the machine was exported -- in violation of Terran law -- to Terra, and it's been played by Terrans.

Intentionally or not, this could be, in fact will soon be, a lethal weapon." He added, "We calculate within the next twenty games. Every time a coin is inserted, the building resumes. Whether a ball gets near the village or not. All it requires is a flow of power from the device's central helium battery. And that's automatic, once play begins." He added, "It's at work building the catapult right now, as we stand here.

You better release the remaining four balls, so it'll shut itself off. Or give us permission to dismantle it -- to at least take the power supply out of the circuit."

"The outspacers don't have a very high regard for human life," Tinbane reflected. He was thinking of the carnage created by the ship taking off. And that, for them, was routine. But in view of that wholesale destruction of human life, this seemed unnecessary. What more did this accomplish?

Pondering, he said, "This is selective. This would eliminate only the gameplayer."

The technician said, "This would eliminateevery gameplayer. One after another."

"But who would play the thing," Tinbane said, "after the first fatality?"

"People go there knowing that if there's a raid the outspacers will burn up everyone and everything," the technician pointed out. "The urge to gamble is an addictive compulsion; a certain type of person gambles no matter what the risk is. You ever hear of Russian Roulette?"

Tinbane released the second steel ball, watched it bounce and wander toward the replica village.

This one managed to pass through the rough terrain; it approached the first house comprising the village proper. Maybe I'll get it, he thought savagely. Before it gets me. A strange, novel excitement filled him as he watched the ball thud against the tiny house, flatten the structure and roll on. The ball, although small to him, towered over every building, every structure, that made up the village.

-- Every structure except the central catapult. He watched avidly as the ball moved dangerously close to the catapult, then, deflected by a major public building, rolled on and disappeared into the take-up slot. Immediately he sent the third ball hurtling up its channel.

"The stakes," the technician said softly, "are high, aren't they? Your life against its. Must be exceptionally appealing to someone with the right kind of temperament."

"I think," Tinbane said, "I can get the catapult before it's in action."

"Maybe. Maybe not."

"I'm getting the ball closer to it each time."

The technician said, "For the catapult to work, it requires one of the steel balls; that's its load.

You're making it increasingly likely that it'll acquire use of one of the balls. You're actually helping it." He added somberly, "In fact it can't function without you; the gameplayer is not only the enemy, he's also essential. Better quit, Tinbane. The thing is using you."

"I'll quit," Tinbane said, "when I've gotten the catapult."

"You're damn right you will. You'll be dead." He eyed Tinbane narrowly. "Possibly this is why the outspacers built it. To get back at us for our raids. This very likely is what it's for."

"Got another quarter?" Tinbane said.

In the middle of his tenth game a surprising, unexpected alteration in the machine's strategy manifested itself. All at once it ceased routing the steel balls entirely to one side, away from the replica village.

Watching, Tinbane saw the steel ball roll directly -- for the first time -- through the center.

Straight toward the proportionally massive catapult.

Obviously the catapult had been completed.

"I outrank you, Tinbane," the lab technician said tautly. "And I'm ordering you to quit playing."

"Any order from you to me," Tinbane said, "has to be in writing and has to be approved by someone in the department at inspector level." But, reluctantly, he halted play. "I can get it," he said reflectively, "but not standing here. I have to be away, far enough back so that it can't pick me off." So it can't distinguish me and aim, he realized.

Already he had noted it swivel slightly. Through some lens-system it had detected him. Or possibly it was thermotropic, had sensed him by his body heat.

If the latter, then defensive action for him would be relatively simple: a resistance coil suspended at another locus. On the other hand it might be utilizing a cephalic index of some sort, recording all nearby brain-emanations. But the police lab would know that already.

"What's its tropism?" he asked.

The technician said, "That assembly hadn't been built up, at the time we inspected it. It's undoubtedly coming into existence now, in concert with the completion of the weapon."

Tinbane said thougtfully, "I hope it doesn't possess equipment torecord a cephalic index."

Because, he thought, if it did, storing the pattern would be no trouble at all. It could retain a memory of its adversary for use in the event of future encounters.

Something about that notion frightened him -- over and above the immediate menace of the situation.

"I'll make a deal," the technician said. "You continue to operate it until it fires its initial shot at you.

Then step aside and let us tear it down. We need to know its tropism; this may turn up again in a more complex fashion. You agree? You'll be taking a calculated risk, but I believe its initial shot will be aimed with the idea of use as feedback; it'll correct for a second shot. . . which will never take place."

Should he tell the technician his fear?

"What bothers me," he said, "is the possibility that it'll retain a specific memory of me. For future purposes."

"What future purposes? It'll be completely torn down. As soon as it fires."

Reluctantly, Tinbane said, "I think I'd better make the deal." I may already have gone too far, he thought. You may have been right.

The next steel ball missed the catapult by only a matter of a fraction of an inch. But what unnerved him was not the closeness; it was the quick, subtle attempt on the part of the catapult to snare the ball as it passed. A motion so rapid that he might easily have overlooked it.

"It wants the ball," the technician observed. "It wantsyou ." He, too, had seen.

With hesitation, Tinbane touched the plunger which would release the next -- and for him possibly the last -- steel ball.

"Back out," the technician advised nervously. "Forget the deal; stop playing. We'll tear it down as it is."

"We need the tropism," Tinbane said. And depressed the plunger.

The steel ball, suddenly seeming to him huge and hard and heavy, rolled unhesitatingly into the waiting catapult; every contour of the machine's topography collaborated. The acquisition of the load took place before he even understood what had happened. He stood staring.

"Run!" The technician leaped back, bolted; crashing against Tinbane, he threw him bodily away from the machine.

With a clatter of broken glass the steel ball shot by Tinbane's right temple, bounced against the far wall of the lab, came to rest under a work table.

Silence.

After a time the technician said shakily, "It had plenty of velocity. Plenty of mass. Plenty of what it needed."

Haltingly, Tinbane stood up, took a step toward the machine.

"Don't release another ball," the technician said warningly.

Tinbane said, "I don't have to." He turned, then, sprinted away.

The machine had released the ball itself.

In the outer office, Tinbane sat smoking, seated across from Ted Donovan, the lab chief. The door to the lab had been shut, and every one of the several lab technicians had been bull-horned to safety. Beyond the closed door the lab was silent. Inert, Tinbane thought, and waiting.

He wondered if it was waiting for anyone, any human, any Terran, to come within reach. Or -- just him.

The latter thought amused him even less than it had originally; even seated out here he felt himself cringe. A machine built on another world, sent to Terra empty of direction, merely capable of sorting among all its defensive possibilities until at last it stumbled onto the key. Randomness at work, through hundreds, even thousands of games. . . through person after person, player after player. Until at last it reached critical direction, and the last person to play it, also selected by the process of randomness, became welded to it in a contract of death. In this case, himself. Unfortunately.

Ted Donovan said, "We'll spear its power source from a distance; that shouldn't be hard. You go on home, forget about it. When we have its tropic circuit laid out we'll notify you. Unless of course it's late at night, in which case --"

"Notify me," Tinbane said, "whatever time it is. If you will." He did not have to explain; the lab chief understood.