The Kentons had just risen from the supper table after a wonderful meal that had featured fresh fruits and vegetables from their own garden. Two days had passed since the adventure in the Great Martian Forest. This was a night of celebration, and Mr. Matthews was present.  
“Now tell us the surprise you had for us, Father,” Jill begged, as they all sat in the living room together. Mrs. Kenton had left cleaning up until later in order to be in on the exciting talk of the evening.
 
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“Not until I know for sure,” Dr. Kenton replied. “I’ll get a phone call in a few minutes about it.”
 
“Can’t you even tell us what it’s about?” Jill went on.
 
“I wouldn’t want to build up false hopes for nothing, Jill,” her father said. “You can wait a little while.”
 
“It was a privilege to eat in such celebrated company tonight,” Mr. Matthews said, with a wink at the children. “You kids will even get your name in the schoolbooks for finding that fabulous city.”
 
“It’s the pilot and Mr. Garland who got us to bail out that should get the credit,” Ted said, with a grin. “If it weren’t for them, we’d never have found the underground city.”
 
“The mural showing the great events in the lives of the ancient Martians was the most important thing of all,” Dr. Kenton remarked. “I was beginning to believe that the greatest riddle of Mars was never going to be solved.” Dr. Kenton had gone to the underground city as soon as he met the young explorers and had heard about their outstanding discovery.
 
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Ted, Jill, and Randy knew the answer now, as did every other colonist on the red planet. The paintings on the wall of the shrine had revealed the baffling riddle. It was simply and clearly portrayed in pictures, just as though the Martians had expected someone someday to know their story. The revelation was that hundreds of years ago all Martians had left their world in large space ships because of Mars’s disappearing oxygen. Apparently there still existed somewhere the remains of a supercivilization which had built these space craft.
 
“Do you think the animals on Mars will finally die out, Dad?” Ted asked, “as the rest of the oxygen combines with the rocks?”
 
“Eventually, I would think,” Dr. Kenton replied.
 
“Where do you suppose the Martians went to find a new home?” Mr. Matthews asked.
 
“They may still be looking,” the scientist replied. “It’s a long way to the stars, remember, and we’re sure they didn’t land any place in our solar system.”
 
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Just then, Yank came bounding into the room. He too had been permitted inside for the celebration. He had been eating his supper in the kitchen. Ted was amazed to see the color bear run up to his father and stand beside him while the scientist scratched his head.
 
“You and Yank are friends!” Ted exclaimed.
 
“We sure are,” Dr. Kenton said. “After you kids left, poor Yank was so lonely he even turned to me. I guess he decided to bury the hatchet when he found out I meant him no harm.”
 
“I wonder why he was so long making friends,” Jill remarked.
 
Dr. Kenton took one of Yank’s forepaws and rubbed back the fur, revealing a scar. “Yank is the fellow I hurt accidentally a few years ago,” the scientist said. “I just thought of checking his paw the day you kids left on your trip.”
 
“He never forgot, did he?” Jill asked.
 
“Not until I’d convinced him I was sorry,” her father replied, rumpling the soft hair of the bear’s head. “His injury was the reason he was alone in the world. He couldn’t keep up with the pace of his friends.”
 
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“Our family is so safe and cozy here,” Mrs. Kenton said, “I hate to think of you going out into that cold wilderness again on a new expedition, John.”
 
“Maybe I won’t be going,” Dr. Kenton said, with a mysterious smile.
 
“What do you ............