Although this book seems geared towards adolescents, it contains adult concepts we will have to learn when we encounter other races out in space. As all of his books appeal to my own sense that it makes no sense that Earth is the only inhabited planet in our solar system, or the galaxy, and all tye myriad of galaxies that exist in our Universe. Either Robert Heinlein was privy to insider information, and he was a brilliant mathematician, or he has the wildest imagination that just happened to hit right on the Truth that Earth is just one little tiny pinpoint of life in our Universe. It's very interesting to me that such a wealth of science fiction about us encountering other life in our Universe seemed to spew out at just the time, the so-called secret space program sent out its alien back-engineered space craft into our solar system beginning in the late 1930's and 1940's, if stories given to us by such whistleblowers as Corey Goode and Randy Kramer, and a host of other military officers and servicemen who have come forward in the past twenty years.At any rate, as usual, Heinlein gives us an enjoyable story about a boy and his Martian pet, and his friend Frank, and mentor Dr. Macrae, and in this book tells us more about the enigmatic Martians from Stranger in a Strange Land, the main reason why i purchased this book. I recommend this story for all Heinlein lovers, and those who enjoy good, clean science fiction so different from the fantasy and gory, battle driven books of today's time. I also enjoy how Heinlein includes social concepts, and following rules outlined for people living on other planets, and how they solve problems they are accosted with in the course of dealing with those whose intentions are not for the good of the society.