feel like placing a bet that she isn't there."
Ignoring the challenge, Dan demanded: "How did you find out all this?"
"Merely by keeping my ears open," Jimmy told him. "I can understand the Martian language as well as I can Terrestrial—better in fact than some of the so-called Earth-lingo that I sometimes hear masquerading as the mother-tongue. These Martian blackguards are notoriously voluble and loudmouthed. All I had to do was listen long enough and I got the whole story. As the mythological detective of yore used to say—it's elementary, my dear Watson—quite elementary."
While his two assistants were talking, Captain Brink had been preparing the Cosmicraft for flight.
"A. Z. for the take-off," he said quietly and the next instant the spaceship was in the air. A few minutes later it alighted in a marsh about half a kilometer from the wok stables at Vanrab.
"It's up to you to figure out a plan for rescuing Miss Andersen, Jimmy," Captain Brink ordered. "Take Dan with you. I'll stay here and guard the Cosmicraft. It will soon be daylight so you'll have to work fast."
"A. Z., Chief," Sullivan responded as he handed Mayer a mysterious bundle without giving him any inkling of its contents. "Come on, Dan. Let's get going."
As they entered the airlock, Captain Brink called to them: "Just a minute, boys. Haven't you forgotten something?"
"I don't think so, Chief," was Sullivan's confident reply.
"How are you going to find your way back to the Cosmicraft?" Brink asked.
"Oh, I have that all figured out," Sullivan told him. With a sly glance at Mayer, he added, "This time—with your kind permission—I shall depend entirely on my own resources. My method will be quite elementary. I shall blaze the trail with a radium pencil. Any objections, Chief?"
Brink countered with another question: "Are you sure that will be safe?"
"Why not?"
"Suppose one of the Martains—or a party of them—sees the luminous marks and follows them to the space ship?"
"I've thought of that too. I intend to place the marks on this side of the rocks along the trail so they will be visible only from the direction of the desert. It is very unlikely that any Martians would approach from that direction."
"A. Z., Jim," Captain Brink smiled. "Good bye and good hunting!"
BY this time it was almost daybreak, and the advance rays of the approaching sun were beginning to paint the dust-laden atmosphere of Mars with faint but grotesque streaks of color. Although no sign of life had yet appeared in the vicinity of the wok stables, the two space marines approaches their goal with prudent caution, taking full advantage of the scanty cover which was afforded by the rocks and sand dunes along the route.
There was no Martian sentry on guard. Since everyone—including the slaves themselves—knew positively that escape was impossible, night guards were considered superfluous. Consequently Sullivan and Mayer were able to enter the slave barracks adjacent to the stables without the slightest difficulty. Both of them were prepared to witness scenes of horror and degradation, but what they ac-
