As many other alternative history works of fiction this book is set in England during the reign of Elizabeth the Great. It was the brightest and yet the most putrid age of British history, a time when history itself could have changed its course: it did, but unfortunately only to a certain extent.
It cannot be a mere chance that so many authors choose this age for their alternative history novels: so many opportunities to make the western world a different place have been wasted then.
(One could add, cursorily, that many fantasy novels seem to be set in an Elizabethan-like kingdom).
These authors seem to have done their research. They give many details about everyday life but they do not overindulge, except perhaps where clothes are concerned; every other real life reference is functional to plot and characterization, not a mean feat indeed.
The plot is interesting, sensible, well contrived. Characters are not as satisfying: Elizabeth is adorable (for a harridan) but everyone else is either shallow or unremarkable or inconsistent or obnoxious for some reason. Sidney is far to obsessed with his protestant faith to be likeable; Marlowe, it goes without saying, could have been a great character but he is such only at times; James is not too bad. All the others play choir when they should have been side kicks. Villains are essentially non existent so that the main characters' very personal demons end by being more interesting.
Writing is professional but not distinguished: several passages are rich of humour or interesting in some way, but there are also problems: the constant shift of POV never signalled by a new paragraph; the constant shift of language register within the same utterance of the same character; some inconsistencies; a wrong use of pluralis maiestatis; some outright grammar mistakes.
Marlowe is a gay character (James is too even if he seems devout to Queen Anne) so gay sex is mentioned but never graphically. The book can be considered safe for teens but I doubt many of them will be interested in the several moral and metaphysical digressions.
This is a nice read, enjoyable and out of print: I recommend you buy it if you find it in some second hand bookstore.