The Lone Sentinel deals with a theme which deeply concerns teen-agers: establishing one's identity as an individual person. Dereske clearly demonstrates that neither Erik's rigid conformity nor Augusta's irreverent individualism provides a satisfactory model for governing one's behavior. When these two extremists compromise and cooperate, they not only rout the alien invaders, but take a large step toward personal maturity.

If development of theme is the novel's greatest strength, inadequate character development is its greatest weakness. The reader finds little more substance to the major characters than Erik can detect inside the Helgatites' spacesuits. There is virtually no physical description of Erik, and his reactions to incidents seem mechanical, motivated more by the demands of plot than by his personality. Despite the inclusion of some details concerning Augusta's appearance, her description too seems generic, and while her behavior generally is more consistent with her personality, there...