The Voynich aspect of the book is straightforward enough: the author buys in to Leo Levitov's whole Cathar Endura ritual reading of the manuscript, along with all the John Dee fairy dust that people like to sprinkle on the VMs to make an otherwise unpalatable mystery taste that little bit sweeter. Yet the author has a character called Dr Noel Branch describe the VMs as "A theurgic riddle in the guise of soft-core pornography" and insisting that the "the key might lie in those silly illustrations" which are usually dismissed as nonsense: which would seen to indicate that Hill has at least properly engaged with the VMs on some level. :-)
But for me, Hill gets enough of the history wrong in important places to break the narrative spell: for example, John Dee was never Emperor Rudolph's alchemist (though Edward Kelly was, and Sinapius / de Tepenecz arguably came close enough too [though one might perhaps call him the "Imperial Distiller"]). Which is a bit of a shame, as this isn't really a key support for the story.
Speaking of the story: in it, Stephan Raszer's job is basically to track down rich women lost in cults, empathize with them, show them his own scarred wrists, have them fall in love with his failed-actor good looks, and convince them to transfer their (implicitly sexual) passion for the cult over to him... so that he can then haul them back to the pampered bland existance in Richville they worked so hard to escape from, thereby earning his handsome fee.
But Raszer is not so much a character as a filmic construct, formed from the unholy merging of a Kundalini/chakra-obsessed later Stevan Seagal (though Raszer never actually fights as such), a later Arnold Schwarzenegger (his "I don't shoot peepul, I only saif cheeldren" phase), and the asexual 1990s James Bonds, who (along with their audiences) were neither shaken nor stirred by the various Dreary Hi-Tech Plot Devices Of Doom placed in their paths.
Females in "Enoch's Portal" fare little better: Raszer's partner comes from the same mop-up-all-the-loose-plot-threads school as did Tom Cruise's impossibly capable assistant in "The Firm" (Holly Hunter); while the empowered modern women Raszer meets are all so, errrm, "enmoistened" by his good looks that they basically make love to him while his soul leaves his body on a brief spiritual holiday. Ghastly stuff.
All the same, there was a good idea in here: though Raszer lives in a supernatural world of walk-ins, succubi, and the like, the cults he deals with are basically spiritual frauds - which leads to an (actually quite interesting) question of whether Raszer is in fact delusional... but this is never obviously addressed.
Really, the problem I had with the book is that (whether it is actually true or not) it comes across again and again as having been written by someone who has watched too many trashy 1990s action movies and taken too many drugs, all the while not really engaging with the world around them. The thought kept returning when I was reading the book that it could all have been redeemed if only the author had done X or pulled back from Y... *sigh*. All in all, I just wish that Hill had had the courage of his convictions and written a screenplay instead, rather than the book of the film in his head. Oh, well!