The question came from Rob, whose voice, try as he would, persisted in faltering. It was an awful feeling to experience, this of being penned scores of fathoms beneath the ocean's surface in a diving boat. "Well, I have a plan in mind. It is a desperate one, but possibly it may work." "What do you propose to do?" This time it was the inventor who propounded the query. Clearly enough Mr. Barr himself could think of no way out of the quandary. "I don't care to say just yet," responded the naval officer. "Why not?" "Because it is a sort of forlorn hope that I don't care to advocate until absolute necessity arises." In the dire extremity into which they were plunged, not one of them cared just then to waste time by asking questions. Clearly Uncle Sam's officer was at the head of affairs. In silence they awaited his next word. "Rob, you must reverse the engines. Give them all the power they will stand. It's just possible that we may be able to back out without injury, although I fear that we are pretty deeply buried in this cliff." Rob, accompanied by Merritt, hastened to obey. Together the two boys entered the engine room, and Rob at once operated the mechanism which caused the _Peacemaker_ to go backward. As he pulled over the lever and the engines began to whirr and buzz, everyone on the boat waited breathlessly for the result. But the _Peacemaker_ did not move. Under the strain of her laboring engines the steel fabric shook and chattered, but not an inch did the diving boat budge. Rob and Merritt exchanged despairing glances. "Can't you get any more power out of her?" asked Merritt anxiously. Rob shook his head. "Not a bit more, old man. She's running at her utmost now." "Then we're stuck?" "It looks that way." "And we're doomed to die right here unless the nose of the boat can be got out of that cliff!" "Never say, 'die,' Merritt. We've done the best we can, and remember the ensign said that he had a plan if all else failed." "Yes, 'a forlorn hope' he called it." "In a case like this we can endure anything. Desperate situations require desperate means to solve them." As the young Scout leader spoke, Ensign Hargreaves burst into the engine room. The engines were still whirring and buzzing, and the hull of the _Peacemaker_ was quivering under their powerful stress. "Have you developed every ounce of power they are capable of?" asked the naval officer. "Yes, sir," responded Rob respectfully; "they can't do another revolution." The officer looked anxious. "In that case, we shall have to resort to my forlorn hope," he said. "And what is that, sir?" asked Rob, his heart beating uncomfortably fast. "Come forward and you shall see." The ensign turned and swung out of the engine room, followed closely by two anxious boys, Rob having waited only to shut off the engines. In the main cabin Mr. Barr, his face white and strained, sat on one of the leather divans. He looked up as the boys and the naval officer entered.