This book (and the movie which derives from it) is remarkable, all the moreso because of the the amount of inadvertent prophecy that takes place during the course of it. 'Shoes of the Fisherman' is a phrase that is sometimes used to refer to the office of the Pope, the Bishop of Rome; the See of Peter, the Chair of Peter, etc., various other historical and scriptural references are a kind of ecclesial shorthand.
This story takes place during the height of the Cold War, when it was not primarily a two-way confrontation, but rather seemed to threaten to become a three-way contest with the seeming emergence of China as a communist power independent from the Soviet Union. This book sets a looming crisis between the United States and Soviet Union as the primary issue, and concludes with a major conference for peace being called (we do not get to know the outcome of this, however, from the book).
Archbishop Kiril Lakato, longtime political prisoner of the Soviet Union, is released (the exact reasoning for this we are never told) by his long-time captors. He is released to Rome, where he is installed as a cardinal for his faithfulness to the church. In quick succession after this, the pope dies, and an election takes place. Remarkably, Kiril the Russian is elected pope, after giving a moving account of his time in captivity to assembled cardinals weary of the election process, and shortly thereafter commits the church to a risky idea of intervention between the major powers, to the dismay of many of the fellow cardinals, who believe the new pope is following a dangerous path.
Subplots include a very timid (by today's standards), and to a certain extent a bit distracting. The main issue (rather than the plot) is to explore the theological issues behind the papal election and the use of theology and politics in the modern church. Despite being written in the 1960s, the book in fact still rings true with many of the facets of this slow-to-change institution.
What makes this book and its attendant film so remarkable is that it was released a full decade before the election of another pope from the communist block. In the 1960s it was considered very shocking to consider a non-Italian pope, much less one coming from behind the Iron Curtain. This of course had the prophetic ring when Karol (not Kiril) from Poland became pope.
Another prophetic instance is in the ecclesiastical trial of the radical theologian -- during his defense, this theologian even uses the words that later theologians would use, who were silenced by the Roman order, and who finally had to leave the church to remain true to their convictions in some instances.
Just how the author could have foreseen these so far in advance is a mystery.