The Enterprise checks in on a small group of scientists in charge of a terraforming project on a lifeless planet. An away team beams down, much to the ire of project head Kurt Mandi (Walter Cotell), who doesn't particularly want to be disturbed. The terraforming project is explained in a fair amount of detail by Louisa Kim (Elizabeth Lindsey, whose performance is so false in the science-expository scenes that it's frankly painful to watch). While on the planet, one of the scientists is killed by a laser drill gone awry. Picard opens an investigation to figure out which of the other scientists programmed the computerized drill to commit murder.
"Home Soil" begins as a homicide investigation before gradually becoming a solid TNG example of hard science-fiction — a story made from equal parts "sci" and "fi" (which is more "sci" than most). Discovered on the planet is a mysterious, glowing, crystal-like substance. The crew brings it back to the lab for study, at which point the story's priorities change.
What makes this episode work is its dutiful attention to the scientific process and a realistic (and often intriguing) portrayal of study and observation. The Enterprise crew members are interested in what lies in front of them and use analysis to find the answers. What they discover is an inorganic intelligent life form — previously considered impossible — which they dub a "microbrain." The microbrain subsequently taps into the computer and threatens the ship.
Okay, so it's not a great episode. The jeopardy premise is routine. The crew's peaceful negotiations are Trekkian-humanistic almost to an overstated fault. The microbrain's personality strikes me as far more arrogant than the humans it's accusing of just that sin (ignorance and arrogance aren't the same thing). But this is an episode that's actual science-fiction as opposed to the phony kind.