ALIENS IN THE FAMILY by Margaret Mahy (Scholastic: $12.95; 174 pp.).

Margaret Mahy’s books belong to that still-unrecognized genre that I call “people books,� books which are not exclusively for children or for adults but for anybody interested in the human dilemma. “Aliens in the Family� can be read on many levels. The story itself is compelling, but underneath the adventures which keep the reader turning the pages is a compassionate study of the deep alienation that besets many people today.

The three human children in the story come from broken--alienated--families. Jake lives with her mother, Pet, on a rundown farm in New Zealand. After the breakup of her marriage, Pet has run home to her parents to be cared for, cosseted, and--well--petted. But her parents are elderly and ill, and need to be cared for. So to Jake falls the job of remembering her grandparents’ medications, chopping the wood, petting Pet.

The summer of her 12th year is to be spent with her father; his new wife, Philippa; 12-year-old Dora, interested chiefly in being (or becoming) beautiful; and 8-year-old Lewis, wounded by too many changes and fascinated with the freedom of eagles, though there are no eagles in New Zealand.

To underscore the sense Jake has of being a stranger in a strange land, Mahy skillfully weaves in the story of Bond, indeed an alien in the science fiction sense of the word. Bond’s people originally came from Planet Earth, but are now on Golgonqua. The vocation of Golgonqua is to make an inventory of all universal knowledge--to be, as Bond sees it, cosmic librarians. Bond has grown up in the School, which prepares students for their mission collecting knowledge, and as the novel opens, he’s about to be sent to Earth for his first test.

The stories come together in a complex and exciting plot. Barely does Bond arrive on Earth when he is attacked by malevolent creatures called Wirdigen, who can shatter time if it gets in their way. Dora sees Bond fleeing from unknown attackers, opens the door of her mother’s car, and the three children, willy nilly, are involved in the effort to save Bond from the Wirdigen.

Looked at in the cold light of reason, the plot is rather implausible. But, as Mahy writes, “Children might believe, as Jake now believed, that Bond was a boy from outer space who was being pursued by enemies. Adults could not believe such a thing. If they did, the world would be changed too much for them to bear.� Challenging us with new concepts and visions, this is indeed a “people book�--stimulating our imagination and helping heal our human alienation.