At some point just after the last ice age, one of the Martians' astronomers brings terrifying news to the Executive Committee. Intelligence has evolved on Earth.
It seems inevitable that the Earthlets will one day notice the entirely dry planet Mars, and, land-bound creatures that they are, leave their mostly wet planet to take up residence in the Martians' back yard. For the Martians the natural solution seems to be to get their retaliation in...