The prologue shows us Bruno's last hours in San Domenico Maggiore, reading a forbidden (not just banned) text in the privy. He escapes mere minutes before an Inquisitor comes for him. His crime is not just that he thinks that earth goes around the sun, but that the universe contains other suns, planets, and possibly sentient species. Parris then jumps ahead 13 years and we rejoin Bruno in London. Within a chapter or two, Bruno gets his marching orders and away to Oxford we go. Almost as soon as he arrives, Oxford dons and students start to probe Bruno, to find out which side he's on and what they can safely say in front of him. Then, the subrector of Lincoln College is murdered, savagely, by a starving deerhound. Bruno begins a sub rosa investigation. Within a few days, two more Oxford men are dead.
Bruno figures out that the men have been murdered to look like martyrs from Foxe's Book of Martyrs (John Foxe's Actes and Monuments). Parris skillfully builds a tense mystery and I didn't see the resolution coming. Heresy is constructed like some of my favorite mysteries. It's told in the first person. We learn what's going as Bruno learns what's going on. Everything, every little clue and slip of speech, makes sense in the end, but there are still twists in the tale as Bruno tries to fit everything together. It's one of the best mysteries I've read for a long time.