A sequel to The Compound, which I have not read. Yet. How to sum up? Teen boy restored, with most of his family, to civilization after living underground for years (see previous book), has a lot to deal with.
Guy meets girl. Girl is a plant or a nudibranch or autotroph or something. More plant, I guess. But not green. Bad Scientist tries to get girl back to The Laboratory. Good/Bad Scientist turns out to be boy's missing father. Good Scientist takes plant girl to a Safe Place.