My favorite Lafferty novel is Fourth Mansions, but this is a close second. Indelible images and ideas from these two books have forever penetrated my brain. I didn't have any good idea of who Thomas More was when I first read Past Master, other than that he had written Utopia and had perhaps meant it to be ironic. Since then, every bright idea for the future is tagged "utopian" (dark visions like Blade Runner are called dystopias).
After seeing the film of the play of A Man for All Seasons, about Sir Thomas More VS King Henry VIII, I'd think of that character when reading Past Master. But not much background is necessary to get the story, such as it is. A future utopia is falling apart, and its leaders ask a computer to find the perfect ruler. With Laffertarian irony, it turns out to be the man who coined the term "utopia" (or popularized it), the mediaeval scholar Thomas More.
Astrobe, the utopia, however, is only sustained so long as people believe in it. Or at any rate, mechanical wolf-like killers are dispatched to eliminate those who lose their belief in the Astrobe dream. The tone, however, is rollicking, with black (noir) humor, and much of the book would be at home on Futurama. Lafferty trumps himself by relating the story through the eyes of Thomas More, a stranger in this strange land. "Lafferty has the power to ignite fire behind your eyeballs," Roger Zelazny noted (or something like that). Laffertarians who've only sampled the short stories, get ready for the full-length ride of Past Master.