The central theme to The Alteration is whether a ten-year-old boy with a superb singing voice should be turned into a castrato to preserve that voice for life at significant cost for the boy - but Kingsley Amis has immense fun with many references to familiar people, books and events, seen in the different light of the tightly Catholic Europe. The strange mix of Tudor and 1970s is done beautifully and atmospherically, as are the many differences between their world and ours (though it's never properly explained why Cowley, now known as Coverley, is the capital, rather than London). There are Protestants in this world - but they are mostly limited to New England, which despite being arguably better than Europe has its own problems.
Altogether a rich and delightful book with enough varied topics (the passage of child to adult, for instance, and the nature of being 'gifted' as well as the obvious social and religious themes) to engage anyone. I do have two issues. The minor one is that it is written in a language that is modern, but with a period feel to deepen that Tudor/1970s mix - which is fine, but distances the reader a little. The rather bigger one is the major plot twist in the final segment of the book - I won't give it away, but this is a twist that will not only have a fair number of readers wincing, but that is so improbable in the context that it makes the ending seem contrived. I understand what Amis is doing here, but he should have found a different way to do it.
Despite that, though, this is a great example of that wonderful mix of science fiction and historical fiction that is an alternative history, and well worth a try.
You can find out more about the book at Amazon.co.uk and Amazon.com