A malice feeds on 'life force' or, in the novel's terms, ground. It is able to mold man-like agents out of wild animals, called "mud-men", and to absorb the knowledge and skills of humans that it kills. The role of the clans of Lakewalkers, descendants of the said near-magical aristocracy, is to patrol the lands around the Dead Lake (remnant of the several Great Lakes) and to kill newly-hatched malices as early in their careers as may be. This they do with knives made from the thigh bones of their own dead, "primed" in the suicide of a mortally wounded or aged Lakewalker so that their death may be "shared" with the otherwise immortal malice. Hence the series title.
The Lakewalker caste's lifeway approximates Native Americans' hunter-gatherer-warrior nomadism after adoption of the horse. East-coast survivors from the commoner caste have been invited by them to re-settle the area south of the Dead Lake. Labelled Farmers for their pioneer farmer lifeway, they have little or none of the Lakewalkers' great talent and tool: "ground sense". With this, it is possible to detect and read details of all living things to a distance varying with individual talent and training --- including the presence of malices. In its absence, Farmers tend to take a jaundiced view of Lakewalkers' activities and abilities, and to discount the role of Lakewalkers in their own survival.