Plastic Girl: Extinction

In Extinction, the second book of the Plastic Girl series, Eva and Iris evade monstrous lifeforms, defeat violent invaders, and unlock evolutionary secrets as they fight for what's left of humanity. Lost in the labyrinth caves below Bear Island, the sisters confront a deadly threat from a longtime ally, the species born of plastic. On the surface, teens from the post-apocalyptic mainland discover the island's long-extinct plants and animals. They quickly divide into factions-those who want harmony with this new life and those who want discord. Only the strongest will survive in this parasitic new world, and one sister will leave the other behind.