Four scientists - including Father Ruiz-Sanchez, a Jesuit and biologist - are sent to planet Lithia in order to produce a report detailing their thoughts about its future possibilities for Earth. Depending on their own interests, they have different views on the planet and its inhabitants, including Chtexa, a lithian metallurgist with whom Ruiz-Sanchez speaks at lenght, and, later, Chtexa's son Egtverchi, who grows up on Earth in the middle of a crisis which he himself aggravates via a TV show he appears in. The focus of the first part of the book is on Ruiz-Sanchez: the fact that Lithians seem to live according to the morals of Christianity without its dogmas forms the bulk of his self-interrogation, although the conflict between religious dogma, pure reason and human passions is only a fraction of the wide range of themes that Blish explores in 'A Case of conscience'. The dual structure of the book is quite clear, and both halves are absolutely necessary: the first, set in Lithia, is mainly concerned with causes (the exploration of Lithia and the mission of the four scientists), and the second, set on Earth, with effects. One could argue that the structure is only apparently dual and that the book's title is only partially correct - every character, from Ruiz-Sanchez to Michelis to Egtverchi, has his/her own case of conscience, something which is underlined not only in the first half of the book, but also in the underrated, complex second half. This is one of those works that can be re-read many times and still reveal new possible interpretations.