"Yes, guess you're right." Jon was also working his handkerchief overtime. "The refrigs in them will keep us cooler, even if they're harder to walk in." "And the suit-goggles will protect us better from the actinic rays of this sun," Jak said. "We're so close--only sixty-five or seventy millions, you said?--that the solar rays are lots stronger than those we get back on Terra, even in the deserts." "Sure, those jungle trees protected us before, so we didn't notice them." Their mother heard them as they returned and came to see what the trouble was. When they explained, as they were putting on their suits, she again warned them to be careful. Then she added, somewhat hastily, "It's just a mother's instinct to keep warning her children to be careful. I know you boys always are--the fact that you came back rather than take chances shows this. Please don't feel badly that I keep nagging at you." "Heck, Mom, we know you aren't nagging." Jon hugged her. "If you ever quit warning us, that's when we'd really get worried." Their suits on and the refrigerators working, the pair began retracing their steps. Jon led the way, since he was carrying the detector. They went in a decreasing spiral to locate the center, then made a beeline for that spot. But after almost a mile the signal seemed to grow weaker, and they stopped for a conference. "Must have passed it," Jon said over his suit-radio as his puzzled eyes studied the meters on the finder. "Try going back thirty or forty yards to the right, then back toward the left," Jak suggested. Soon Jon shouted and started off in a new direction, but more slowly, and Jak ran quarteringly toward him. Inside half a mile Jon lost the beam again, and once more they quartered to find it. In narrower and narrower circles they searched. Suddenly Jak stumbled and fell to the ground. As he started to rise, Jon heard his excited yell coming through his earphones. 6 At his brother's eager cry, Jon ran over toward where the older boy was stooping down, examining carefully something almost completely embedded in the sand. He saw Jak rise, take his shovel from the carrying straps on his suit's back, and start uncovering whatever it was he had stumbled over. As Jon came up, he uttered an exclamation of surprise. "Why ... what ... that's a metal plate. What is it, Jak?" "Don't ... know ... yet," the elder panted as he worked even more feverishly with his shovel. Jon quickly laid down the detector, which was clicking excitedly, to unsling his own shovel and begin digging. In a few moments they had completely bared the metal plate, and could now see it was about ten by four feet, and hinged on one side. "Looks like a trap door." "Sure does. Lend a hand--let's see if we can open it."