Plastic Girl: Extinction. Plastic Girl, #2

Extinction is the suspenseful second book in the Plastic Girl series. Sisters Eva and Iris transform their isolated island from wasteland to paradise, They stop a gang of nomadic teens from taking it over. Now, lost deep in the caves below Bear Island, they will evade monstrous lifeforms, defeat violent invaders, and unlock evolutionary secrets as they fight to protect their new world.  The species born from plastic can heal the entire planet and reverse the climate apocalypse but not without sacrificing Eva and all of humanity.
In the spirit of Lord of the Flies, those on the island will either work together or kill each other. One sister will leave the other behind, testing the ties of their found family. Another more symbiotic way forward for these competing species is revealed but proves even more terrifying than extinction.