40. Speaker For The Dead, Orson Scott Card.

This is the second book in the Ender's Game series. Ender is called upon to travel to Lusitania, a planet colonised by a limited population of Portugese Catholics, and inhabited by a new race, the pequeninos, who show sentience, but are being observed only, with very limited cultural or scientific influence. He is there to speak the death of Pipo, a xenologer who was studying them before his death at their hands. Ender has to determine whether the pequeninos are fundamentally capable of coexisting with humans (and whether humans can coexist with them).

This book is a lot more philosophical than Ender's Game, and a lot less action-packed. It's still very good, but not in the same fashion. It explores the concept of a hierarchy of closeness, going from 'the same species on the same planet', 'the same species on a different planet', 'a different species that we can nonetheless communicate and reason with', and 'a different species that we cannot communicate or reason with', with the idea that it's only morally correct to destroy beings of the last group, varelse, if the choice is to let them live to destroy other life, or destroy them first.

It also goes quite far into what family is, and what can make up a family, by studying a local woman, Novinha, and her children, who are all inextricably entangled with the pequeninos, and thus, Ender. Again, the interpersonal relationships are complex and satisfying, and the new characters are quickly just as dear as the older.