This is the second of the Giants novels, after Inherit the Stars. In the first novel, a body is found inside a space suit on the moon--and turns out to be 50 thousand years old. Later, on Ganymede, is found a derelict alien ship, with the remains of alien giants--and it turns out to be 25 million years old. These are the central mystery around which the story revolves, and the interesting part is the play of scientific ideas. In other worlds, the novel his hard science--pretty hardcore. In the second novel, those aliens, the "Gentle Giants of Ganymede" return. Unlike one of the reviewers on LibraryThing I didn't find them a disappointment. It's true, when it comes to creating complex characters, human or otherwise, well, it's not Hogan's forte. But his ideas are, and I found the Ganymeans interesting foils for humans, and found the interplay of ideas very lively--in fact, I thought there were less dry patches here--with the information more skillfully delivered through story. And, I admit, I found the denouement fitting and rather moving. I can see her why Isaac Asimov thought Hogan was an author with promise in his early days.