In this second book of the trilogy, Tom must continue aiding Harlan Ames and the former slaves-now free citizens-of the Lunar Colony. As Harlan seeks answers to the disappearance and origin of the Empress in Tibet, Tom is working on a project to help both the colony and the entire state of California, both going through severe water shortages and both needing almost immediate relief His plan is to capture a water-laden comet from outside the orbit of Jupiter, bring it into orbit high over the Moon, mine the ice and then let the water processing facilities of the colony purify it. Then, all he needs to come up with is a way to get the clean water down to Earth. Harlan finds more than he bargains for when he comes upon a woman with the personality of a young girl who has been severely injured. He nurses her back to health, eventually taking her back with him to the Moon. But, what he unleashes might spell the end of thousands of lives. Tom faces success and setbacks as a few of the loyal former Elite members of the colony sabotage his efforts to help save the colony. This is the action-packed sequel to Tom Swift and His Space Battering Ram.