The follow up to Tom Swift and the Space Battering Ram, the action begins with an upcoming environmental disaster in California happening at the same time Harlan Ames decides to Search for answers about the Empress Shangi-La, believed to have perished in deep space. He finds a lot more than he set out to. Like, a woman with two personalities who has a near fatal metallic piece sticking out of her head. And a grave. And the remains of a long dead father. Oh, and she used to be the Empress, but now seems to mostly be a child. Meanwhile, Tom sets out to capture an ice-bearing comet to bring into either Earth or Lunar orbit in the hopes of being able to mine the ice and deliver the water to the Earth. There are many obstacles to overcome, not the least of which is how to get it down through the atmosphere to where it is needed. With time running out, Tom takes a big gamble and brings a huge comet into lunar orbit. The next problem is getting the ice cleaned at the colony and back down to the Earth. But to make things just a bit more difficult, the Empress returns to the Moon with plans to regain her strangle hold on the former slaves, now free colonists. Unless Harlan and Tom can manage to stop her.