The environmental theme appears in The Night the Heads Came, but it is not as well developed as it is in The Beasties. In The Night the Heads Came, an evil group of being from another world, the Others, thrive on environmental catastrophes. On Earth, they try to push people toward making irrational decisions about their environment so that Earth will become poisoned and polluted beyond redemption. The environmental motif appears only near the end of The Night the Heads Came and is of slight importance to the novel as a whole. It differs significantly from the environmental theme in The Beasties in that in The Beasties the source of environmental destruction is solely human, not inspired by outside forces, and the invaders are the human beings, whereas the other beings, far from being aliens, are natives of the earth.

Much of Sleator's work has focused...