James Blish, "A Case of Conscience"

Mankind has made first contact and among the four researchers sent to investigate the garden-world Lithia and its reptilian inhabitants is Father Ramon Ruiz-sanchez, SJ. The Jesuit botanist and doctor is the only member of the research team to oppose opening the world up for human intercourse. The Lithians, he suspects, may be too good to be true. Indeed, with their peaceful and proseprous society, more advanced in many ways than man, and in their total lack of any idea of faith or the divine, they imply that a sentient species can live the good life without religious revelation. These "unfallen" beings are not angels. Indeed, he fears, they may be a creation of the Devil, meant to tempt man into abandoning religion in light of their enlightened example.

But this belief is heresy. Only God has the power of creation. The Devil merely perverts. If these beings are good, they cannot be a creation of the Devil. Yet why would God create them perfect without religion, while making man imperfect in His image?

Father Ruiz-Sanchez returns to Earth with a precious and frightening cargo, the unhatched egg of a Lithian. Blessed with a genetic memory, his passenger will hatch and mature without Lithian care. But what will happen to an alien raised among men?

The result is horrific; a brilliant, cynical, conscience-less creature who wreaks havoc on human society, manipulating men like a demonic puppet-master plying his craft. His presence on Earth provokes riots and incites murder. Meanwhile, it appears that Lithia is largely made up of weapons-grade lithium, an unimaginable source of thermonuclear munitions. And now the human-raised Lithian has outsmarted his hosts and is on his way back to Lithia, perhaps to cause a fall from grace among his kin akin to the kind that the serpent brought Adam in Eden.

This vivid, imaginative, fast paced, and often poetic work is a book of ideas. The characters are three-dimensional and the situations are quite topical in a timeless way certainly still valid fifty years after it brought its author a Hugo Award for best novel. If you haven't read Blish start here.

The painting is "Lilith" by John Collier.