THE first hint about the robot trouble on the planetoid Pallas to reach us came from that intrepid reporter of interplanetary news, Sandra de Long. Sandra had been on Pallas investigating the plutonium mines there.

She hadn't been on the trail of any specific story, but just sort of writing a book about the major asteroids and their scenic interests. Pallas. you know, has the only natural deposit of pure plutonium in the solar system—outside of the debatable and inaccessible claims made for certain mountains on Neptune's smaller moon. Because plutonium is the stuff from which atomic reactors are made, it's valuable and still pretty expensive to fabricate, even in this day and age, two hundred and fifty years after the Manhattan Project.

Plutonium, being highly radioactive, is mined exclusively by robots. They are directed from the mining settlement of Valiersdorf, where the Terrestrial technicians and reduction engineers live. Sandra had sent back two stories about the rough-and-ready life of the mining town—mostly pure invention, since the pioneering days have long been past and the hermetically enclosed town is as comfortable as any suburban hamlet on Earth.

Bur Sandra had an eye for odd detail and she had ferreted out some of the older artifacts, and one of the worked-out pits. and had poked her shapely nose into the robot warrens too. In her last broadcast she had spoken of trouble with the robots. There was a steadily increasing number of inexplicable errors in their work. One technician had already expressed the thought that the radioactivity of the mines was impairing their mechanism

Sandra had suggested that perhaps exposure to the vast power of the plutonium had altered the delicate atomic chargings of the robotic brains. Robots, as you know, are thinking beings in u way—they are equipped with mechanical brains that can and do transact elementary reasoning, enough for their lobs. These brains are fairly delicate and are always enclosed in a transparent shell where their dials I and adjustments can he periodically checked.

The next thing we of the Asteroid Patrol knew, word came that Pallas had suddenly gone out of communication with the rest of the universe. Our ships were ordered there.

About our space cruiser there was plenty of speculation about the mission. Ted Winston, our commander, was specially worried, and as his lieutenant, I knew what was bothering him. It wasn't robot trouble, it was Sandra. They were engaged.

When our vessels came in sight of Pallas, everything seemed quiet. True, there was no sign of life in the mines. the doomed town seemed strangely silent and lightless. but nothing was exploding.

We settled for a landing near the town, when the first robot battery opened up on us! It was a near thing, it was what we had expected. The blast of an atom-heat ray just missed our ship—had it hit us, we'd have blown up and that would be the end of this story. But it missed, doubtless because of inexperience and because it wasn't a true weapon. It was a mining beam, up-ended, and being worked as a gun.

We got out of its range and made a landing in a small valley between two tiny Pallasian stony hills.

Pallas is like the rest of the asteroids, a bare. lifeless rocky world. None of these tiny planets have the gravity to hold down an atmosphere, and you can't walk about without a space mask and your own portable air supply.

Ted and I took counsel as to what to do next The question was who had shot at us and why. Someone had to go out and investigate and it would have to be us. Then Sparks came in and told us there was a message coming in.

It was from the robots. They had announced their independence. they were going to hold the mines and earth crew as hostages. and they were willing to release Sandra de Long to us as evidence of their good faith. Sandra, they announced, would be able to give us the dope on their demands.

It was clear, just the same, that the brains of the robots were cracked. Just the way the thing was worded was proof of it. They couldn't hope to win. Still, Ted told me, if we could get Sandra clear, he'd feel a lot better about dealing with the situation. For of course we could not make a deal with these lunatic machines.

Ted told the robots by radio to bring Sandra to the ship and he would meet them. They must come unarmed. They agreed.

We didn't want Ted to chance it, but he insisted. Sandra was his girl and he wasn't going to let someone else risk her rescue. He put on his air helmet, took his gun, and left the ship; the rest of us watching with baited breath from the ship's observation ports.

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Coming towards the ship we could now see a robot and it was carrying something. It came closer. We gasped.

The metal man was carrying Sandra like a sack of potatoes, slung under one arm! The poor girl was wiggling and apparently yelling for help.

Ted Winston stood like a man struck. The sight was certainly calculated to drive him nuts. He couldn't dare attack the robot now, even though he could see the thing was armed and that if it got too close the machineman could probably destroy our space ships with a good blast—or at least ground them.

Ted was in a spot, and I didn't envy him. He couldn't dare fire, for his shot would destroy Sandra too. He couldn't dare not fire, in spite of robot promises, because the ships and his men were in danger. The robot had violated its promise and was armed.

It was an old gangster trick—the helpless hostage as a shield for the killer.

Then Ted Winston did what we never expected. He dashed forward, raised his flame pistol, and fired! Fired pointblank at the robot—and at Sandra!

The robot sizzled for a moment. and then suddenly the robot simply exploded! There was a terrific flash and when the dust cleased, there was only a hole in the ground and little bits of metal and Sandra scattered about! But Ted somehow didn't seem appalled at what looked to us like a cold-blooded act of murder—how could he kill his own fiancee like that?!

We dashed out of the ship, armed, and surrounded him. And then in a few words we understood.

Ted had saved us all. For he had recognized the robot plot and we had not. The thing we thought was Sandra was not her at all—it was a cunningly constructed robot—designed to look like Sandra and actually loaded with enough plutonium to blow our ship to smithereens. It was the intent of the robots to hand her over to is, to have Ted bring her aboard our ships under the impression it was Sandra, and there to blow ourselves up when the dummy detonated!

But how had Ted caught wise to all this? Simple, when you think of it, and a robot wouldn't think of it. They don't have to breathe, you know. It never occurred to them to put an air helmet on their dummy Sandra. But Ted knew that the real Sandra couldn't have survived out there in the airless surface of Pallas, couldn't have yelled as the phony Sandra did, couldn't have been so obviously active in the robot's clutches! So he destroyed them both.

How we rescued the real Sandra and the Pallas rebellion collapsed is a story you all know from your history books. But the story of Ted Winston's clever act of deduction is probably new to you.