After bringing the inhabitants to Eros and learning the creature's language through Boyd Allen's amazing new computer that can translate any language and imprint it into the mind, the Space Explorers find that if the creatures are not returned to their planet soon they will die. After finding of their home planet through the use of the Observatory, the two creatures are returned home.

Upon arriving at their home planet, however, the Space Explorers discover a band of ruthless men that are burning their cities and capturing hundreds of the creatures. It is up to the Space Explorers to see if they can stop this ruthless band of men and return order to the once peaceful planet. 

This book basically continues the story that The Forgotten Star began. The book begins with the three space explorers (Jim Barry, Ken Barry, and Dig Allen) returning to the newly-discovered asteroid Eros (which is now their home) after a thorough studying space flight and all it entails.

This book, in my opinion, is the best book of the series. No other book can match its artwork, or its story, or the book's execution. If you only had a chance to read one of these books, read this one. Sure, it's not completely scientifically accurate -- Mercury, after all, does NOT always keep one of its faces toward the sun but rotates as any other planet would.

When the Explorers wanted to learn the language of the aliens, all they had to do is get the alien to recite all the words for different nouns, adjectives, pronouns, and other parts of speech. A picture dictionary was brought out, and as the alien looked at each picture he would recite the word for that object or action. The machine would then pick up on that, and after it had enough information it would gather its information together. Once it was ready, the person who wished to learn the language was put to sleep, and while he was asleep the machine "wrote" the language into his brain.

The idea of such a machine is quite an interesting one. Wouldn't it be nice if you could learn French or German or Chinese without any effort at all on your part? For that matter, it seems that you could learn anything this way. Simply get the facts together, haul out your Langivac, and let things roll. Rote memorization of facts would be a thing of the past.

I need hardly say that this machine won't be appearing at your nearest wholesaler any time soon. True, the idea doesn't break any physical laws, but it's impractical, all the same. How do you "write" knowledge into a person's brain? How does a person's brain store information, anyhow? How can a computer "figure out" a language? These are crucial questions that must be answered before such a machine can be made. Maybe in a few hundred years these problems will be solved, but until then, we'll have to stick with learning things the old way.

Another point that crops up in the book -- which ties in closely with what I just said -- really reflects the totally unpredictability of science. In the book, the little green men were needed to put machines -- most notably computers -- together. It seems that, in 2100, computers, control panels and the like were made of huge tangles of wires and connectors. Connecting those wires by hand was very difficult. The little green men, however, could do it relatively easily, quickly, and accurately, which spelled increased profits to the computer makers.

This prompts a question. Why were the computers of 2100 still using large copper wires? Where was the author's vision, or insight? Couldn't the author of the book see that, in just 10 short years, the microchip would be invented that would enable entire computers to shrink to the size of a postage stamp, or a deck of cards? Of course not. Microelectronics was not even conceivable before it came about. No one could foresee huge, monstrous computers that took up entire rooms shrinking enormously while becoming thousands of times faster. It just wasn't conceivable. It was a physical impossibility -- until it happened.

So many old science fiction books I have read have had this same flaw. Spaceships to Venus sent messages by rolls of tape -- not electronics. Radios and computers still worked on vacuum tubes. It just goes to show, really, that we cannot predict the future of physical science with any kind of accuracy. Just because it is impossible today does not necessarily entail that it will remain impossible. Science fiction books have been, and will continue to be, inaccurate. But, hey, if they weren't, wouldn't it be a dull world?

5 stars out of 5. This is an excellent book: in my opinion it is the best of the series. The book starts out with an exciting opener, and it keeps the suspense high until the satisfying end. The dangers are unique and creative, and the cast of characters and locations are at their best. The little green men were a brilliant idea, and their home was a fantastic piece of insight: it's a shame he was proven wrongÖ