This is an extraordinarily detailed and sophisticated analysis of Galileo's trial before the Roman inquisition in 1633 and has as its audience people well-versed in the ‘Galileo Affair’. Anyone not already deeply engaged with Galileo's encounter with the inquisition would find it difficult to read. The first third of the book offers a detailed account of the procedures of the inquisition and an examination of the events of 1615 and 1616. Throughout the text Speller engages the views of other scholars, notably Stillman Drake, Annibale Fantoli and Francesco Beretta. He is critical of Beretta's thesis that the decisions of the inquisition and the Index of Forbidden Books, especially in 1616, represent a ‘doctrinal determination by the Pope’ rather than disciplinary injunctions. Speller argues that a key to understanding the actions of Pope Urban viii and the inquisition can be found in Urban's comments to Francesco Niccolini (the Tuscan ambassador to Rome) and to the commission the pope named in 1632 to examine the newly published Dialogue concerning the two chief world systems. The pope told the commission that it must weigh ‘every minutia, word by word, since one is dealing with the most perverse subject one could ever come across’. According to Speller, the pope's chief concern was the threat to the doctrine of divine omnipotence involved in any attempt to consider the motion of the earth to be absolutely true, rather than as a mere mathematical hypothesis. As we know, it was precisely an argument in defence of divine omnipotence which Galileo was required to include at the end of the Dialogue. The pope feared that any claim that a particular view of the heavens was ‘necessarily true’ would contradict the theological position that God was all-powerful and was not under the necessity to order the heavens (or anything else for that matter) in any particular way. At the trial, those favourable to Galileo (for example Cardinal Francesco Barberini, the pope's nephew) had always to keep in mind the pope's principal concern. Speller thinks that many of the inconsistencies and inaccuracies evident in the trial proceedings can be accounted for by recognising that there were these different factions in the inquisition. In this respect, we might understand how it is that passages of the final sentence against Galileo contain the incorrect view that Copernican astronomy had been declared (in 1616) in some solemn way to be heretical. One of the strengths of the book is the detailed analysis of important texts (often citing the original Italian or Latin). Despite his frequent citing of secondary sources, Speller does not refer to the work of William Wallace who has done so much to examine the kind of science that Galileo embraced. This is an especially odd omission in that so much of Speller's thesis depends on the issue of whether or not Galileo defended the new astronomy as being ‘absolute truth.’