A Case of Conscience is part of that odd subgenre of Catholic Theological Science Fiction. Father Ramon Ruiz-Sanchez is a Jesuit, a biologist, and one of four members of a human commission evaluating the planet Lithia for interstellar colonization. Lithia is home to an intelligent alien race, 12 foot tall reptiloids with advanced mastery of genetics, microbiology, ceramics, and semiconductors, but rudimentary knowledge of chemistry and atomics physics. More curiosly, their culture can only be described as Edenic. There is no war, no politics, a single planetary language, ecological balance between the verdant jungle and the Lithians. The problem is that this perfection may hide a deadly sin.

The first section of this book concerns the expedition's final days on Lithia, following Father Ramon as he cares for partner and wanders around the city. The drama is the four-sided debate between the expedition members. Physicist Cleaver has a plan to turn the planet into an interstellar arsenal, using the natives as slave labor in hydrogen bomb factories. Michaelis and Agronski believe in a moderate position that the planet could be a useful waystation for trade in complex biological molecules. Father Ramon, however, has arrived at the radical position that the Lithian society too closely matches Christian precepts to exist by accident, and that the planet must be an elaborate trap created by Satan. The sinless Lithians lack souls, and would tempt mankind towards an evil path. The commission deadlocks on whether Lithia should be opened or closed, with the matter referred to higher authorities on Earth. As Father Ramon leaves, a Lithian that he has grown close to gives him a present: a jar containing a Lithian embryo which will grow to maturity by the time it reaches Earth.

The second half of the book follows events on Earth, where all is not well. As a reaction to the threat of atomic annhiliation, humanity has retreated to vast underground Shelters. Nationstates have collapsed as such, replaced by local Shelter authorities and a barely capable UN. Living in the tunnels has induced a kind of species-wide madness, with a third of the population near schizophrenic. Into this tinderpile is dumped the young Lithian, Egtverchi. A voracious reader, he masters every human form of rhetoric without any ethical center whatsover, and becomes a planetary TV personality popular with children and the insane masses. Egtverchi attends a wildly decadent party hosted by a corrupt aristocrat, and then proceeds to announce that he is a citizen of no country but his own mind, and that his followers should join him in passive resistance. This prompts the largest riots in the history of Earth, and Egtverchi escapes back to Lithia. Meanwhile, Ramon is defrocked for the Manichean heresy, Michaelis gets married to the biologist Liu Meid, and Cleaver's plan to turn Lithia into a hydrogen bomb factory is approved. In final chapter, Ramon exorcises the entire planet of Lithia through an experimental FTL telescope as Cleaver turns on the first components of his factory. The entire planet is engulfed in an explosion, but whether it was Ramon's faith or an error in Cleaver's equations is unclear.

On the plus side, this novel takes its ethical stances seriously, and does a great job at distinguishing them. In particular, faith is treated with a great deal of respect, with the Jesuit tradition of scientist-explorer-missionary carried out into space. Cleaver's militarism is coherent within its limits. In all cases, the ethics of belief are contrasted strongly against various forms of nihilism; the ultimate ends of quantum physics of 'holes inside nothing', and Egtverchi's de Sadian individualism and mass delusions. The status of alien souls is something that the Catholic Church has actually thought about, and it's up to the reader to decide if the Lithia are sinless, fallen, or soulless. The first half of the novel (originally published as a novella) is incredibly tight and interesting. Unfortunately, the second half doesn;t quite have the same focus or heft. Blish was well-read, and Finnegan's Wake is used as a repeated motif, but he may have taken the ambiguity too far.

An encounter with aliens is both a judgment on them, and a judgment on humanity. Egtverchi clearly judges humanity unworthy, and he may be right about the Shelter society depicted. But Earth endures, and it is Lithia that is wiped out in a blaze of divine wrath/thermonuclear fire, which seems somehow unfair. The second half of this book is a dissapointment, but the strong first half and opening of ethical and theological questions makes it a solid serious read.