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.

As little as a month ago there had been no thought of the danger, no barest notion, until it exploded in the face of Earth's government. Steadily and methodically the Council of Science had been cleaning up the nest of robot spies that had riddled Earth and its possessions and whose power had been broken by Lucky Starr on the snows of Io [2].

It had been a grim job and, in a way, a frightening one, for the espionage had been thorough and efficient and, moreover, had come within an ace of succeeding and damaging Earth desperately.

Then, at the moment when the situation seemed completely in the clear at last, a crack appeared in the healing structure, and Hector Conway, Chief Councilman, awakened Lucky in the small hours one night. He showed signs of hurried dressing, and his fine white hair was in rumpled disarray.

Lucky, blinking sleep out of his eyes, offered coffee and said in amazement, "Great Galaxy, Uncle Hector" (Lucky had called him that since his early orphaned days, when Conway and Augustus Henree had been his guardians), "are the visiphone circuits out?"

"I dared not trust the visiphone, my boy. We're in a dreadful mess."

"In what way?" Lucky asked the question quietly, but he removed the upper half of his pajamas and began washing.

Bigman came in, stretching and yawning. "Hey, what's all this Mars-forsaken noise about?" Recognizing the Chief Councilman, he snapped into wakeful-ness. "Trouble, sir?"

"We've let Agent X slip through our fingers."

"Agent X? The mysterious Sirian?" Lucky's eyes narrowed a bit. "The last I heard of him, the Council had decided he didn't exist."

"That was before the robot spy business turned up. He's been clever, Lucky, darned clever. It takes a clever spy to convince the Council he doesn't exist. I should have put you on his track, but there always seemed something else you had to do. Anyway____________________"

"Yes?"

"You know how all this robot spy business showed there must be a central clearing agency for the information being gathered and that it pointed to a position on Earth itself as the location of the agency. That got us on the trail of Agent X all over again, and one of the strong possibilities for that role was a man named Jack Dorrance at Acme Air Products right here in International City."

"I hadn't known this."

"There were many other candidates for the job. But then Dorrance took a private ship off Earth and blasted right through an emergency block. It was a stroke of luck we had a Councilman at Port Center who took the right action at once and followed. Once the report of the ship's block-blasting reached us, it took only minutes to find that of all the suspects only Dorrance was out of surveillance check. He'd gotten past us. A few other matters fit in then and-anyway, he's Agent X. We're sure of it now."