At times the book reminded of Wolf Hall. That too was written in the first person, and if not actually in blank verse it often felt like it. The Marlowe Papers is not so versified that you don't often think it is actually just plain prose.
Once you sort out the chronology of what is going on, the story is quite gripping. It seems entirely plausible that Marlowe fell foul of various pressures. He was a much more serious thinker and writer than Jonson, but too revolutionary. And getting mixed up in spying is always going to be a dangerous move.
Having just read the Jonson biography by Donaldson, the contrast between the two men is fascinating, both came from relatively "humble" backgrounds. Although, back then a proper trade like shoemaking (Marlowe) or bricklaying (Jonson), if you were successful, is not at all what we today might think of them.
The book will lead me to read a leading source or two for the idea that Marlowe really did write the Shakespeare canon, even if like for the man from Stratford himself, the Earl of Oxford, Francis Bacon and Mary Sidney there is still zero contemporary and relevant personal evidence that any of them wrote the works (see the almost unarguable work of Diana Price, "Shakespeare: The Unorthodox Biography").
While waiting for real, hard evidence to turn up on the authorship question, we will just have to sit back and enjoy the best of the speculative works, of which Ros Barber's book is definitely up there among them.