Mr. Benjamin cried out and barely squirmed out of the way of the charging animal. The force of the unicorn’s thrust caused him to bury his sharp horn to the ground. He withdrew it with a grunt of fury and shook black earth from the glossy white tip. Then he retreated for another charge. [Illustration: _The unicorn rushed up the slope, his head lowered and his frightening ivory horn poised for attack._] “Help me!” Mr. Benjamin cried desperately, scrambling madly to get a foothold in the slipping gravel. By now Jim was within arm’s reach of the tourist. He braced himself against the boulder that had settled into a hollow and strained forward to grasp Mr. Benjamin’s hand. Just as the man was pulled to his feet, the unicorn struck again, burying his horn in the ground barely inches below the tourist’s boots. Jim shuddered as he hurried Mr. Benjamin up the slope to safety. “My poor camera!” the tourist groaned. “It’s down there with that animal!” “You’re lucky not to be down there with him yourself, Mr. Benjamin,” Babe said grimly and led the party back toward the car. Next the car passed over the fascinating Lake of Steam. A mist, like the sheerest of veils, rose in a solid sheet from the depths to a height of half a mile, shot through with every imaginable color. Jim thought it an incredibly beautiful sight. Jim took over running the car while Babe went back with the passengers to point out more of the picturesque wonders. Jim was surprised when suddenly the car began roller-coasting down a steep slope toward a forbidding dark opening in the cliff face. Quickly he realized that this was the famous Haunted Tunnel of Venus. Jim switched on the headlights Babe had told him about and slowed the car with a burst of the forward jet. Slowly the car entered the enchanted cavern. The darkness seemed to make Jim’s ears keener. Presently there came to him the mysterious sighs and groans that had given the tunnel its name. Although he knew this was caused by wind whistling through the opening and the shifting of rock strata, it nevertheless caused chills to run up his spine. All at once an unexpected loud buzz from the radio set shocked him into an involuntary cry. As his nerves calmed, he switched on the radio and spoke into the mike, “Yes?” “Let me speak to Steward Hogan,” came a brisk voice that Jim knew could belong only to Captain Coppard. “Yes, sir,” Jim replied. He opened the door of the cabin and called Babe. Jim saw a flashlight advance toward him down the dark aisle. “It’s Captain Coppard,” Jim whispered. “Hogan speaking,” Babe said into the mike. “Steward,” the chief officer of the _Hercules_ said, “who is the young man with you?” Jim’s heart seemed to give a final quiver and go dead inside of him. “Jim Vance, sir,” Babe answered. “I don’t find him on my roster of personnel,” snapped the officer. “He isn’t on it, sir,” Babe admitted manfully. “Then he’s a stowaway?” “Yes, sir,” Babe said reluctantly.