The Sun was a brilliant diamond in the sky, just large enough to the naked eye to be made out as something more than a star; as a tiny white-hot pea-sized globe.

Out here in the vastness of space, near the second largest planet of the Solar System, the Sun gave out only one per cent of the light it cast on man's home planet. It was still, however, the brightest object in the sky, as four thousand full Moons would be.

Lucky Starr gazed thoughtfully at the visiplate which centered the image of the distant Sun. John Bigman Jones watched with him, an odd contrast to Lucky's tall and rangy figure. When John Bigman Jones stretched himself to his full height, he stood five foot two exactly. But the little man did not measure himself in inches and he allowed people to call him by his middle name only: Bigman.

Bigman said, "You know, Lucky, it's nearly nine hundred million miles away. The Sun, I mean. I've never been out this far."

The third man in the cabin, Councilman Ben Wes-silewsky, grinned over his shoulder from his place at the controls. He was another large man, though not as tall as Lucky, and his shock of yellow hair topped a face that had grown space-brown in the service of the Council of Science.

He said, "What's the matter, Bigman? Scared way out here?"

Bigman squawked, "Sands of Mars, Wess, you get your hands off those controls and say that again."

He had dodged around Lucky and was making for the Councilman, when Lucky's hands came down on Bigman's shoulders and lifted him bodily. Big-man's legs still pumped, as though carrying him toward Wess at a charge, but Lucky put his Mars-born friend back in his original position.

"Stay put, Bigman."

"But, Lucky, you heard him. This long cobber thinks there's more to a man just because there's more of him. If that Wess is six feet tall, that just means there's an extra foot of flab... "

"All right, Bigman," said Lucky. "And, Wess, let's save the humor for the Sirians."

He spoke quietly to both, but there was no questioning his authority.

Bigman cleared his throat and said, "Where's Mars?"

"On the other side of the Sun from us."

"Wouldn't you know," said the little fellow disgustedly. Then, brightening, "But hold on, Lucky, we're a hundred million miles below the plane of the Ecliptic. We ought to be able to see Mars below the Sun; peeking out from behind, sort of."

"Uh-huh, we should. Actually, it's a degree or so away from the Sun, but that's close enough for it to be drowned out in the glare. You can make out Earth, though, I think."

Bigman allowed a look of haughty disgust to cross his face. "Who in space wants to see Earth? There isn't anything there but people; mostly groundhogs who've never even been a hundred miles off the surface. I wouldn't look at it if that were all there was in the sky to look at. You let Wess look at it That's his speed."

He walked moodily away from the visiplate.

Wess said, "Hey, Lucky, how about getting Saturn on and taking a good look at it from this angle? Come on, I've been promising myself a treat."

"I don't know," said Lucky, "that the sight of Saturn these days is exactly what you might call a treat."

He said it lightly, but for a moment silence fell uneasily within the confined pilot room of The Shooting Starr.

All three felt the change in atmosphere. Saturn meant danger. Saturn had taken on a new face of doom to the peoples of the Terrestrial Federation. To six billion people on Earth, to additional millions on Mars, the Moon, and Venus, to scientific stations on Mercury, Ceres, and the outer moons of Jupiter, Saturn had become something newly and unexpectedly deadly.

Lucky was the first to shrug off that moment of depression, and, obedient to the touch of his fingers, the sensitive electronic scanners set into the hull of The Shooting Starr rotated smoothly on their universal gimbals. As that happened, the field of vision in the visiplate shifted.

The stars marched across the visiplate in steady procession, and Bigman said with a curl of hatred in his upper lip, "Any of those things Sirius, Lucky?"

"No," said Lucky, "we're working through the Southern Celestial Hemisphere and Sirius is in the Northern. Would you like to see Canopus?"

"No," said Bigman. "Why should I?"

"I just thought you might be interested. It's the second brightest star and you could pretend it was Sirius." Lucky smiled slightly. It always amused him that the patriotic Bigman should be so annoyed because Sirius, home star of the great enemies of the Solar System (though themselves descendants of Earth-men), was the brightest star in Earth's heavens.

Bigman said, "Very funny. Come on, Lucky, let's see Saturn, and then when we get back to Earth you can get on some comedy show and panic everybody."

The stars kept their smooth motion, then slowed and stopped. Lucky said, "There it is-unmagnified, too."

Wess locked the controls and twirled in the pilot's seat so that he might see also.

It was a half-moon in appearance, somewhat bulging into more than half, just large enough to be seen as such, bright with a soft yellow light that was dimmer in the center than along the edges.

"How far away are we?" Bigman asked in astonishment.

Lucky said, "About a hundred million miles, I think."

"Something's wrong," Bigman said. "Where are the rings? I've been counting on a good look."

The Shooting Starr was high above the south pole of Saturn. From that position it should see the rings broad on.

Lucky said, "The rings are blurred into the globe of the planet, Bigman, because of the distance. Suppose we magnify the image and take a closer look."

The spot of light that was Saturn expanded and stretched in every direction, growing. And the half-moon that it had seemed to be broke up into three segments.

There was still a central globe, half-mooned. Around it, however, touching the globe at no point, was a circularly curved ribbon of light, divided into two unequal halves by a dark line. As the ribbon curved about Saturn and entered its shadow, it was cut off in darkness.

"Yes, sir, Bigman," said Wess, lecturing, "Saturn itself is only seventy-eight thousand miles in diameter. At a hundred million miles, it would just be a dot of light, but count in the rings and there are nearly two hundred thousand miles of reflecting surface from one end to the other."

"I know all that," said Bigman indignantly.

"And what's more," continued Wess, unheeding, "at a hundred million miles, the seven-thousand-mile break between Saturn's surface and the innermost portion of the rings just couldn't be seen; let alone the twenty-five-hundred-mile break that divides the rings in two. That black line is called Cassini's division, you know, Bigman."

"I said I know," roared Bigman. "Listen, Lucky, that cobber is trying to make out I didn't go to school. Maybe I didn't get much schooling, but there isn't anything he has to tell me about space. Say the word, Lucky; say you'll let him stop hiding behind you and I'll squash him like a bug."

Lucky said, "You can make out Titan."

At once Bigman and Wess said in chorus, "Where?"

"Right there." Titan showed as a tiny half-moon about the size, under current magnification, that Saturn and its ring system had appeared to be without magnification. It was near the edge of the visiplate.

Titan was the only sizable moon in the Sarurnian system. But it wasn't its size that made Wess stare at it with curiosity and Bigman with hate.

It was, instead, that the three were almost certain that Titan was the only world in the Solar System populated by men who did not acknowledge the over-lordship of Earth. Suddenly and unexpectedly it had been revealed as a world of the enemy.

It brought the danger suddenly closer. "When do we get inside the Saturnian system, Lucky?"

Lucky said, "There's no real definition as to what is the Saturnian system, Bigman. Most people consider a world's system to include all the space out to the distance where the farthermost body is moving under the gravitational influence of that world. If that's so, we're still outside the Saturnian system."

"The Sirians say, though... " began Wess.

"To Sun-center with the Sirian cobbers!" roared Bigman, slapping his high boots in anger. "Who cares what they say?" He slapped his boots again as though every Sirian in the system were under the force of his blows. His boots were the most truly Martian thing about him. Their raucous coloring, orange and black in a curving checkerboard design, was the loud proclamation that their owner had been born and bred among the Martian farms and domed cities.

Lucky blanked out the visiplate. The detectors on the ship's hulls retracted, leaving the ship's outer skin smooth, gleaming, and unbroken except for the bulge that ringed the stern and held The Shooting Starr's Agrav* attachment.

Lucky said, "We can't allow ourselves the luxury of the who-cares-what-they-say attitude, Bigman. At the moment the Sirians have the upper hand. Maybe we'll get them out of the Solar System eventually, but right now the only thing we can do is to play it their way for the while."

Bigman muttered rebelliously, "We're in our own system."

"Sure, but Sirius is occupying this part of it and, pending an interstellar conference, there isn't anything Earth can do about it, unless it's willing to start a war."

There was nothing to be said to that. Wess returned to his controls, and The Shooting Starr, with minimum expenditure of thrust, making use of Saturn's gravity to the maximum, continued to sink rapidly toward the polar regions of the planet.

Down, down, deeper into the grip of what was now a Sirian world, its space swarming with Sirian ships some fifty trillion miles from then [1] home planet and only seven hundred million miles from Earth. In one giant step Sirius had covered 99.999 per cent of the distance between itself and Earth and established a military base on Earth's very doorstep.

If Sirius were allowed to remain there, then in one sudden moment Earth would sink to the status of second-class power at Sirius's mercy. And the interstellar political situation was such that for the moment all of Earth's giant military establishment, all of her mighty ships and weapons were helpless to deal with the situation.

Only three men in one small ship, on their own initiative and unauthorized by Earth, were left to try, by skill and craft, to reverse the situation, knowing that if they were caught they could be executed out of hand as spies-in their own Solar System by invaders of that Solar System-and that Earth could not do a solitary thing to save them.