While there is a lot to like in this theological science fiction novel from the late 1950s, I ultimately found it a bit of a slog. Blish starts us off on Lithia, a far-off planet inhabited by very large sentient lizard-like creatures that have a perfectly moral, crime-free society and yet no religion at all. The scientists from Earth that have been sent to review the planet for future exploration include biologist / Jesuit priest Ramon Ruiz-Sanchez. He is fascinated by the biology and sociology of this new world but has a break in his admiration for the planet when he is struck by the belief that the planet was created by Satan as a lure for humanity to turn away from the grace of God. I think. Honestly, the theological parts lost me a bit (sorry, Seminary friends!). When the men get ready to go back to Earth, one of the Lithians that Ruiz-Sanchez has befriended gives him a baby Lithian in a jar to raise on Earth. As this Lithian grows up severed from the moral compass of his home planet, he absorbs all the weird energy of an Earth that has retreated to an elaborate series of underground bunkers in fear of nuclear war, a decadent society of ultra-rich folks, and a growing number of viscerally discontented workers. Things come to a head when the young Lithian uses his charismatic popularity to call his discontented followers into an open rebellion against the government, ultimately leading to a rather neat solution to Father Ruiz-Sanchez's dilemma (and impending excommunication).

The best parts of this book are definitely the descriptions of Lithia and the extremely detailed exploration of the unique biology of the planet. The worst parts are the cringingly racist and sexist descriptions of the Asian scientist who helps raise the baby Lithian, and the Trump / Q-like influence of the Lithian on this future Earth (I just didn't have the energy for that -- ymmv). In between are the religious factors, which may or may not be your jam depending on how philosophical, theological, or Catholic you are. And if you know what Manichaeism is without having to look it up.