Through these hoops sped the single-car trains of the Mars-Tube, every four minutes through every hour of the long Martian day. The electrostatic emanations from the hoops held the cars nicely balanced against the pull of gravity; save only when they stopped for the stations, the cars never touched anything more substantial than a puff of air. The average speed of the subway, stops not included, was upwards of five hundred miles an hour. There were no windows in the cars, for there would have been nothing to see through them but the endless tunnel wall slipping smoothly and silently by.
So easy was the completely automatic operation that the men from Earth could scarcely tell when the car was in motion, except by the signal panel that dominated one end of the car with its blinking lights and numerals.
Stanton led Annamarie to a station with ease and assurance. There was only one meaning to the tear-drop-shaped guide signs of a unique orange color that were all over Mars. Follow the point of a sign like that anywhere on Mars and you'd find yourself at a Mars-Tube station—or what passed for one.
Since there was only one door to a car, and that opened automatically whenever the car stopped at a station, there were no platforms. Just a smaller or larger anteroom with a door also opening automatically, meeting the door of the tube-car.
A train eventually slid in, and Stanton ushered Annamarie through the sliding doors. They swung themselves gently on to one of the excessively broad seats and immediately opened their notebooks. Each seat had been built for a single Martian, but accommodated two Terrestrials with room to spare.
At perhaps the third station, Annamarie, pondering the implications of a passage in the notebook, looked up for an abstracted second and froze. "Ray," she whispered in a strangled tone. "When did that come in?"
Stanton darted a glance at the forward section of the car, which they had ignored when entering. Something—something animate—was sitting there, quite stolidly ignoring the Terrestrials. "A Martian," he whispered to himself, his throat dry.
It had the enormous chest and hips, the waspish waist and the coarse, bristly hairs of the Martians. But the Martians were all dead.
"It's only a robot," he cried more loudly than was necessary, swallowing as he spoke. "Haven't you seen enough of them to know what they look like by now?"
"What's it doing here?" gulped Annamarie, not over the fright.
As though it were about to answer her question itself, the thing's metallic head turned, and its blinking eyes swept incuriously over the humans. For a long second it stared, then the dull glow within its eye-sockets faded, and the head turned again to the front. The two had not set off any system of reflexes in the creature.
"I never saw one of them in the subway before," said Annamarie, passing a damp hand over her sweating brow.
Stanton was glaring at the signal panel that dominated the front of the car. "I know why, too," he said. "I'm not as good a linguist as I thought I was—not even as good as I ought to be. We're on the wrong train—I read the code-symbol wrong."
Annamarie giggled. "Then what shall we do—see where this takes us or go back?"
"Get out and go back, of course," grumbled Stanton, rising and dragging her to her feet.
The car was slowing again for another station. They could get out, emerge to the surface, cross over, and take the return train to the library.
Only the robot wouldn't let them.
For as the car was slowing, the robot rose to its feet and stalked over to the door. "What's up?" Stanton whispered in a thin, nervous voice. Annamarie prudently got behind him.
"We're getting out here anyhow," she said. "Maybe it won't follow us."
But they didn't get out. For when the car had stopped, and the door relays clicked, the robot shouldered the humans aside and stepped to the door.
But instead of exiting himself, the robot grasped the edge of the door in his steel tentacles, clutched it with all his metal muscles straining, and held it shut!
"Damned if I can understand it," said Stanton. "It was the most uncanny thing—it held the door completely and totally shut there, but it let us get out as peaceful as playmates at the next stop. We crossed over to come back, and while we were waiting for a return car I had time to dope out the station number. It was seventh from the end of the line, and the branch was new to me. So we took the return car back to the museum. The same thing happened on the trip back—robot in the car; door held shut."
"Go on," said Ogden Josey, Roentgenologist of the expedition. "What happened then?"
"Oh. We just went back to the library, took a different car, and here we are."
"Interesting," said Josey. "Only I don't believe it a bit."
"No?" Annamarie interrupted, her eyes narrowing. "Want to take a look?"
"Sure."
"How about tomorrow morning?"
"Fine," said Josey. "You can't scare me. Now how about dinner?"
He marched into the mess hall of the expedition base, a huge rotunda-like affair that might have been designed for anything by the Martians, but was given its present capacity by the explorers because it contained tables and chairs enough for a regiment. Stanton and Annamarie lagged behind.
"What do you plan to do tomorrow?" Stanton inquired. "I don't see the point of taking Josey with us when we go to look the situation over again."
"He'll come in handy," Annanarie promised. "He's a good shot."
"A good shot?" squawked Stanton. "What do you expect we'll have to shoot at?"
But Annamarie was already inside the building.
II
Descent into Danger
"Hey, sand-man!" hissed Annamarie.
"Be right there," sleepily said Stanton. "This is the strangest date I ever had." He appeared a moment later dressed in the roughest kind of exploring kit.
The girl raised her brows. "Expect to go mountain-climbing?" she asked.
"I had a hunch," he said amiably.
"So?" she commented. "I get them too. One of them is that Josey is still asleep. Go rout him out."
Stanton grinned and disappeared into Josey's cubicle, emerging with him a few moments later. "He was sleeping in his clothes," Stanton explained. "Filthy habit."
"Never mind that. Are we all heeled?" Annamarie proudly displayed her own pearl-handled pipsqueak of a mild paralyzer. Joseph produced a heat-pistol, while Stanton patted the holster of his five-pound blaster. "Okay then. We're off."
The Martian subway service was excellent every hour of the day. Despite the earliness, the trip to the central museum station took no more time than usual – a matter of minutes. Stanton stared around for a second to get his bearings, then pointed. "The station we want is over there – just beyond the large pink monolith. Let's go."
The first train in was the one they wanted. They stepped into it, Josey leaping over the threshold like a startled fawn. Nervously he explained, "I never know when one of those things is going to snap shut on my – my cape." He yelped shrilly: "What's that?"
"Ah, I see the robots rise early," said Annamarie, seating herself as the train moved off. "Don't look so disturbed, Josey – we told you one would be here, even if you didn't believe us."
"We have just time for a spot of breakfast before things should happen," announced Stanton, drawing canisters from a pouch on his belt. "Here – one for each of us." They were filled with a syrup that the members of the Earth expedition carried on trips such as this – concentrated amino acids, fibrinogen, minerals and vitamins, all in a sugar solution.