[1] This children's book is set in a beach community in California, as well as on a tiny, habitable moon, "Basidium", in an invisible orbit 50,000 miles from Earth.

He has been a traveler around the world for many years, and when he finds out about the mushroom planet, he decides to rebuild the boys' lost spaceship and return to what he knows is his ancestral home.

Earlier, the boys had written a letter to a nearby university professor inviting him to come and give a lecture to their young astronomers' society.

This book is much more topical than the last one was, as Peabody insists that the Mushroom Planet must be explored and exploited "for the good of science" — as well as for his own personal glory.

Mr. Peabody ends up committing an act of sacrilege on the Mushroom Planet that almost gets everyone involved killed, and in general annoys and scares all.