Environmentalism has been a motif in Sleator's earlier novels (for instance The Night the Heads Came; 1996 see separate entry, Vol 9), but in The Beasties, it becomes important for the motivations of the characters. In The Beasties, a botanist takes his family to spend the summer in a large house in a forest, where he can study fungus. The forest is being chopped down by lumber companies, leaving hillsides denuded of trees and most other kinds of life. However, the trees are not disappearing peacefully: Something in the forest resists the loss of the trees, resulting in destroyed lumber company equipment and, horribly, in maimed people who mysteriously at night lose arms, legs, ears, noses, and other parts of their anatomy, without waking up or sensing anything amiss before morning. Those responsible for the atrocities may be the mysterious beings who may just be folklore creatures called "the beasties."