The main theme of Rats is that of a corrupted environment. Sarah believes that the rebellion of the rats is a logical outcome of people despoiling the land: "People had ruined the water and the land and the air for as far as she could see. Oil-and-greasecovered barges lined a dead black shore.

Everything was endangered. Crawling.

Dying." Sarah and Michael are shown to be on the right side of the battle over the environment by their selling candy to raise money for a bird sanctuary. Sarah in particular has a strong interest in natural history and wildlife, and Michael's research into wild rats proves essential in the war against the rats from the local dump.

Environmental issues appear in other Zindel novels. For instance, in Loch, youngsters try to save some ancient animals from extinction at the hands of adventurers, and in Reef...