DAVE RANDALL stood a short distance away from the customary crowd, and looked out across the vast paved plaza of the Chicago Spaceport. The night was dark and moonless, but out there under the floodlights everything seemed a confusion of activity. Endless lines of electric trucks were hauling the cargo aboard the Martian Princess, and near the spaceship tall cranes were in operation.

Randall leaned on the iron railing and watched, fascinated. And he was just a little awed at the thought that when the ship hurtled up and away from Earth he would be in it.

Suddenly Randall felt his arms pinioned to his sides in a tremendous grip, and he jerked backward off his feet. He opened his mouth to yell. A large hand closed over it. He felt someone's hot breath on his neck. He writhed and struggled with all the strength of his six feet of hardened muscle, but the assault had been too sudden, and he was off balance. Then the hot breath was close to his ear and a voice whispered warningly:

"Shhh! Thalia!"

At that word Randall immediately ceased struggling. So--it was "Thalia" already, huh? The grip loosened and the hand came away from his mouth. Randall whirled around, but his assailant put a finger to his lips and nodded meaningly toward another figure walking casually away in the darkness.

"All right," Randall said in a low voice, but angrily. "You've got the password, but did you have to come at me in that way?"

The man looked a moment longer at the third figure walking away, then turned to Randall. A wry smile was on his lips.

"See that man? He's been staying close to you all evening. So have I: but I've been watching him. I saved your life just now, young fellow. I saw him try to get you with a blaster, and I had to act quickly! Sorry if I was rough."

"An atomic blast!" Randall gasped. "But they're outlawed, they're--" and then he stopped suddenly, confused and conscious that he sounded frightened and a little childish.

His rescuer was still smiling grimly, and he answered very simply: "Yes. Now you know what you're up against. I'd advise you to keep in the light, with the crowd."

But now Randall was smiling too, with his lips but not his eyes. In the clear gray depths of those eyes was something grim, and there was a stubbornness in the way he held his chin.

"Then why," Randall demanded a bit pugnaciously, "didn't you tackle him instead of me? Don't ever do that again."

The other man shrugged. "Those weren't my instructions. Isn't your life worth anything to you?"

"Come over here in the light," Randall said, "I want a better look at you!"

They walked toward one of the field lights. Randall saw a man a good two inches taller than his own six feet, very dark, and with a suggestion of wiry strength which Randall had already felt demonstrated. The man wore huge green glasses, but Randall studied the face beneath, trying to memorize it.

"Then suppose you tell me what were your instructions," Randall said. "You've got the word all right--Thalia. But how do I know--"

"Those weren't my instructions either," the man said, still smiling; but as he saw swift anger come across Randall's face he added quickly: "But I don't mind obliging. In your pocket you have a letter. This letter was handed to you by Felix Reynolds, President of Inter-Continental Stratoplane Lines, with certain explicit instructions for delivery on Mars. Right so far? He also told you to trust any person who approached you with the word 'Thalia', but under no circumstances to surrender the letter to any but the proper hands. Furthermore--"

"That's enough, I'm satisfied," Randall said with a disarming frankness. He was far from being satisfied, but he wanted the fellow to think so. "But I wish you'd have let me go after that fellow who took the blast at me. Damn uncomfortable feeling, and now he's liable to do it again! What about him, is he making the trip?"

"Of that I'm certain."

"Are you?"

The man didn't answer, but looked at Randall with that enigmatic smile that was fast becoming annoying. Then, without another word he turned swiftly and walked away into the crowd.

Randall started to follow, but hesitated. Then he called, "Thanks!" The man looked swiftly back, his glasses flashing greenly, and Randall was sure he saw that curious smile still on his lips. He shrugged with an uneasy little laugh.

"Well," he said aloud, "it's begun! I had an idea things were going to happen, but not this soon!" His hand went automatically to his inside coat pocket, and he felt the bulk of the mysterious letter that was fastened securely there. Satisfied, he walked over to the inner gate, showed the guard his pass, and sauntered onto the field.

It was still a few hours until take-off time.

Randall stood in the half-dark at one end of the loading platforms. The ten-minute signal had just sounded, and he was trying to make up his mind whether to go aboard now or wait until the last minute. He laughed softly to himself as he remembered his mysterious rescuer's advice to keep in the light. He preferred to keep in the gloom where he could see, but not be seen. From here he commanded a view of the inner gate through which the passengers had to come.

Just as he decided nothing else was going to happen tonight, and that he'd better get aboard--he saw the girl. She had just come through the gate with the last-minute passengers. She pressed hurriedly past the guard, nervously stuffing her pass back into a handbag. She hesitated, peering back into the crowd anxiously. Then, instead of going to the waiting-room with the others, she hurried toward the shadow of the platform where Randall was standing. Again she glanced back nervously as though fleeing from someone, trying to reach the shadow before being spotted.

Randall followed her gaze to the gate. Then he straightened up, suddenly very interested. For, pressing through the throng, he saw--the man in the green glasses! It was the same man, Randall was sure. The fellow snatched his pass back from the guard and hurried forward, peering into the crowd searchingly. The girl had seen him too, but she had reached the shadow now. She stopped only a few feet from Randall; her hand went nervously to her throat, and she sighed with relief when she saw her pursuer go the other way.

Randall looked back at the girl--just in time to see the electric truck bearing down swiftly and silently upon her. "Look out!" he shouted. At the same time he sprang forward and jerked her out of the way just as the truck whizzed by.

She uttered a little gasp and looked up at him with wide, startled eyes, too surprised to speak.

"Whew!" Randall said. "We have to be careful tonight, don't we?" There was a double meaning in his words. He nodded back toward the gate and said, "It's all right; he didn't see you."

The girl stared at him a moment longer before she sprang swiftly away without uttering a word. But into her eyes had flashed a look that told Randall she knew what he meant.

And Randall frowned, for in those eyes had been something else. He was sure of it. It had been a momentary flash of--recognition! So the girl knew him, then! But Dave Randall was very sure he had never in his life seen her before...

He stared after her, still frowning puzzledly. Then he smiled. For it hadn't been too dark there in the shadow, and as he thought of that white and frightened face--but a very pretty face!--he suddenly realized he wanted to know her better.

And he was very sure he was going to...