Spock is injured in an explosion while studying soil samples from Belle Terre, and realizes that the soil in being infested with siliconic gel, which will expand to a height of five miles over the planet, suffocating the inhabitants. They come to realize that the infestation must have begun with the lone Kauld ship that the Enterprise had destroyed when it had appeared to be attacking the planet. At first it is planned to evacuate the colonists, but that soon proves impractical, since most of the ships have been stripped to assist the colonists in establishing themselves on the planet. A plan is put into effect to convert a desert valley into a covered refuge for the colonists, and Scotty and his team manage to make a couple of the Conestoga ships suitable for taking some of the colonists onboard. Most of the colonists are saved, but some (including Lilian) die in the siliconic gel. The cometary body where Yanorada (the brains behind the siliconic gel attack) is hiding is revealed when the Kauld military send ships to protect it. Kirk organizes an attack on the base to try to find the key to disabling the nanoassemblers that are creating the siliconic gel, but it turns out the code was computer generated and even Yanorada doesn’t know it. But Spock mindmelds with Yanorada and ascertains how to extract the code from the computer. Then the job begins of clearing away the siliconic gel.