The hero of what is proposed to be a mystery series shouldn't be on the dull side. It may be that the author was hesitant to mess too much with Bruno, as he was a real person. Parris also falters a bit with the character of Sophia, who is at first introduced as a "modern" woman, but whose actions soon seem to follow the lines of a lovesick romantic novel heroine. There is subtle humor in the novel, such as Cobbet's mangy old cur having the name of "Bess."
Parris does capture the absolute unrest and danger the religious schism caused in England, even many years into Elizabeth I's reign. Catholics were forced to live under cover, much like Protestants did in the reign of Elizabeth's sister Bloody Mary. Those found guilty of heresy, identified as a Papist, or Catholic, were subjected to a truly horrible death, which Parris is only too willing to describe in detail.
There is a subplot that concerns a very special book by Hermes Trismegistus, but it's mostly forgotten as the gruesome staged murders and Bruno's detection take center stage. Bruno's spying for Secretary Francis Walsingham and the Elizabethan court opens the door for subsequent novels (the second novel Prophecy, has just been released in the U.S.), but unless the thrills get amped up, I'm not sure how much demand there would be for this series. In Heresy there is a bit too much concentration on the tortuous manners of deaths at Lincoln College at Oxford and less on fleshing out the character of Giordano Bruno. But Bruno moved on in his life, traveling and teaching and publishing his writings throughout Europe, so the series would have to as well.