Frederick Rolfe styled himself Fr. Rolfe to write this book, to make it look as if he was a Priest. Rolfe himself failed to enter the RC priesthood, rather like Mr Rose/Hadrian (the hero)... and from there on, you can see from his life that Hadrian VII is really Rolfe's wish fulfilment... not only to become a priest, but a Pope! Like Hadrian/Rose, Rolfe was an oddball in real life.
Mr Rose is a reclusive, catty & bookish Englishman, who excels in verbosity and likes showing off his skills in Ancient Greek. Through a chain of coincidences, this autistic "hermit" ends up becoming a priest, and then Pope. He renames himself Hadrian as the last English Pope before him, Nicholas Breakspear, had. Once in power Hadrian takes two conflicting courses, first reforming the Vatican to become less worldly and selling off some of its treasures for charity, harmonising RC factions etc and secondly getting right into world politics... this novel was written before WWI so some of his solutions are a little quaint. He gets France and Russia "sorted out", and hands over most of the world to his native England (see end). Hadrian has a strong anti-socialist bent, but this book came about 8 years before the Bolshevik Revolution occurred.
The other characters are less appealing... least convincing is Jerry Sant, who is supposedly some kind of Scottish socialist, but who speaks neither like a Scot nor much like a socialist (devious or otherwise). Cardinal Ragna, who might be presumed to supply some decent opposition, is also a cardboard cutout.
Rolfe has an odd style of writing... for example he refuses to talk of people being "Scottish" or "Irish", but prefers talking of them as Pictish, Erse or Gaelic, or Keltic (with the K). Despite being a pompous quoter of Classical Greek (and more oddly not mentioning much Latin to go with it), he shows a great prejudice towards living languages of his country's neighbours. -
"England is the dominant race: her language is the language of all her colonies. Why a triplet of little conquered countries [Scotland, Ireland and Wales] should refuse to learn English - should be permitted to insist on their barbarous and unliterary languages, we could never understand. They are conquered countries annexed to their conqueror"
Rolfe evidently needed educating in this area. Gaelic monks taught the Anglo-Saxons how to read and write, and the Irish Free State began a mere six years after the book was written, but I digress. Here is a specimen of the book's style, which goes on and on, page after page -
"The Supreme Arbitrator provided the human race with scope and opportunity for energy. The provisions of the Epistle to princes were drawn up in the Form of Treaty dividing the world, til Midnight (G.T.) of December 31st (N.S.) of the year 2000 of the Fructiferous Incarnation of the Son of God into the Ninefold Kingdom, the American Republic, the Japanese Empire and the Roman Empire."
(This is his cabbalistic way of saying Hadrian handed over Africa and most of Asia to England "the Ninefold Kingdom", naturally, and had given Siberia to Japan. The Roman Empire he speaks of is Continental Europe controlled by the Kaiser.)