The Martians start as bouncers, metamorphose into adults, then continue their life after death as "old ones" (see Stranger in a Strange Land). While living on the physical plane, they inhabit both worlds: the physical and the (unspecified) other. Members of the Unification Church note that this concept corresponds to their doctrine of physical world and spiritual world with human beings having both a physical body and a spiritual body.
When an unscrupulous headmaster seeks to prevent the annual migration of families to save the Company money, two boys run away from school to warn their parents. In a foreshadowing of many revolutions against bad authority, an uprising against the company forces retakes the school and effects the needed migration. The crusty Doctor MacRae and the two boys are heroes, but the relationship between one bouncer (kept as a pet) and the boy who "owns" him is the real key to this book. Absent that friendship, the Martians would have exterminated all the human colonists.