I picked this up in a secondhand bookshop while travelling, because the book I'd been intending to read turned out to have a sick serial killer of a narrator, one who seemed to find killing amusing.
Proteus, of course, is now a fairly old book (1979) and occasionally that's obvious in the text. Its subject matter is still relevant - the corruption at the heart of many nations' governments which results in innocent people being incarcerated and tortured without reason. (Guantanamo Bay is a prime modern example.)
In terms of the story, West takes on a huge challenge, and I'm not sure that it comes off. His main character, John Spada, is a super successful businessman whose only child marries an Argentinian journalist, a man who's already in trouble with his government because of his outspoken writings. But Spada is also the undercover leader of an organisation whose main aim is to free innocent people who've been convicted of no crime but are a 'nuisance' to the State, and he performs this other role well, using his money freely, and being able to work with the people in the know who can make a difference. His organisation is reportedly very large yet somehow they all manage to keep their group invisible.
Things go awry for Spada, as they must in any good book, and instead of continuing on a benevolent path, rescuing innocent people, he turns to a kind of vigilante approach. I guess West is saying that even the best people can be corrupted by frustration with evil; certainly Spada, for all his integrity, goes downhill in due course in a way that I didn't find particularly believable. I'm sure other reviewers have given better synopses of the plot, so I won't expand on it here.
So why only 3 stars? West's characters lack real personality somehow; he gives them ticks and traits, but they don't come alive. There are dozens of characters in this book, because the subject matter and plot have considerable breadth, but they all speak with a similar voice: they're likely to slip from saying plot-moving statements to intoning the theme at the drop of a hat. Even in books, people don't preach to this extent. And it's often hard to tell where West's loyalties lie: in his own life he had an on-off relationship with the Catholic church, and most of his Catholic main characters are pretty loose in their religion; they don't really seem to present much of a faith. West had huge concerns about corruption, as is evident here, but the book swings all over the place, and poor old John Spada is swung around with it. He has reason to be deeply angry but the way his morals change doesn't quite ring true.
In spite of my criticisms I found the book surprisingly readable (as most of West's other books have been); even when my critical mind was saying - 'I don't believe that bit' - my reading mind wanted to keep on reading, to see what happened. Personally I found what happened rather disappointing: the climax is BIG, in keeping with the rest of the book, but it's not believable: it's Hollywood, rather than West.