Rome, 1633. Galileo Galilei, sixty-nine and ill, has been carried to the Holy Office on a litter. The charge they can name is a piece of paper from 1616. The offence they cannot name is the book in which he put the pope's own argument into the mouth of a fool. Vincenzo Maculano, Commissary General of the Holy Office, is a military architect and a hard prosecutor. Handed the charge without the reason, he reads the book to the end, and finds something nobody in Rome has noticed. The proof at the heart of it does not work. What he does with that, in a courtyard, walking an old man round an orange tree, is the business of this novel. Every date, document, decision and outcome here is the historical record's. The conversations are invented. Galileo's Inquisitor stands alone and reads in an evening. Readers who want the documented history behind it will find it in Galileo Galilei: What Counts as Proof, published the same day.