Ruth Rendell, according to the quote featured prominently on the dustjacket, called Patricia Finney `the le Carre of the sixteenth century' - after reading this, I think I'd've preferred a touch more of Forsyth about the book.
As other reviewers have noted, the story is structured so that different chapters are told from the perspective of different characters. This approach has advantages in drawing us into the private worlds of the protagonists. It also, in Finney's use, slows the pace dreadfully at times. Effectively, we get the whole story from each of the viewpoint character's perspective, which can include lengthy recaps of the story we've already read from another character's point of view. Some incidents, which involve more than one of the characters, can be repeated two or three times. Conventionally, authors interchange between points of view more regularly and achieve the effect of giving different perspectives on the same incident by telling it once allowing other characters to reflect on significant acts to show their attitude. That tends to heighten pace and tension. Finney's technique serves to hold back both and removes any real feeling of climax from the book's dénouement, due to it being split between more than one narrative.
All of which is a shame because, if you can make it past an irritating introduction, where the author speaks to us directly as a modern reader, there is some terrific writing here. The horrors of the slave ship, the rower's bench on a galley and the paranoia of the secret world of Elizabethan politics are effectively captured. There are justifiable complaints one could make - contrary to the assumption here galleasses were a well known class of ship for both the English and Spanish, a member of the Inquisition is likely to recognise the signs of Jewish heritage just as easily as the reader, the central mystery rather too easy to guess - but these tend to be forgivable.
Something of mixed bag, then.