Like Rashomon it tells the story of a murder from four different points of view. Each narrator has a reason to dissemble. You reconstruct the 'truth' from the four 'fingerposts' of narrative. This is an interesting intellectual exercise in itself.
The other interesting exercise is to reconstruct a modern understanding of what is happening (a character 'has a mental illness', a character 'is a homosexual') which would not be described in those terms by the characters themselves. In that respect it is interesting in the way an SF story can be, describing a society which thinks differently. Of course a lot of this is guesswork - almost everything we read from the 17th century is infused with strong religious faith. Was this the reality of people's interior lives? Or was it a shallow convention of discourse?
The final narrative was the least satisfactory for me, and somewhat undermined the power of the book. This section is presented as the true fingerpost. The narrator of this section is a Mary Sue, though likable. In this section the things we had worked out for ourselves are spelled out (plus plenty of things I hadn't worked out) and this is always a bit of a letdown.
The story is satisfyingly complex, and intricate like a watch. Most of the characters are historical, like Boyle and Locke. Their divergent motives and perspectives are well described and make them dissemble and deceive themselves. Knowing those tendencies, you can work out the true events from their deceptive accounts. Ultimately I would have preferred some of that complexity to have been retained, and the book ends with a 'truth' that is daring and big, but doesn't satisfy me.