The story revolves around Jack, a translator/subtitler who, while working on a near-untranslatable Russian film, stumbles upon an unreadable (and unapologetically Voynich-like) manuscript. Many of the other characters are librarians or collectors of obscure aphorisms, who seem to share his delight not so much in etymology, but in the living texture of language, its flow. However, the book's central irony is that though Jack can read many languages, he cannot read the people around him: while their lives are complex and conflicted, his is empty - and so he allows the strange manuscript to fill his void.
Of course, while at first he can make no sense of it, under UV light its margins yield many clues to its provenance and history: and as Jack becomes progressively more attuned to its nuances and strange ur-language, it begins to reveal details to him of a fantastical machine to build, not entirely unlike a medieval version of the one in Carl Sagan's novel "Contact" (you know, the one filmed with Jodie Foster).
I have to say that at one point while reading Vellum, I did find myself completely immersed: this was when Jack's growing obsession for his pet manuscript (and his disconnection from the world) suddenly lurched and exceeded my own. I felt the urge to try to pull him back from going over the brink: perhaps this was Matt Rubinstein's focus for the book, to help readers find and explore the point where they felt uncomfortable with the change in Jack's downward arc.
Though it has a contemporary European vibe to its vocabulary, Vellum is firmly situated in the Australian geographical and historical landscapes (spinifex, First Fleet, etc): and is all the fresher and more engaging for it. The paradoxical idea of an inland desert lighthouse recurs through the book, and (surprisingly to me) one such does exist, at Point Malcolm: I think this nicely mirrors various Voynich-like conundrums, which I'm sure you can work out for yourself.
In short, I like Vellum: though not perfect (plot-wise, the explosion is a bit clumsy, for example: and half-quoting Foucault's quoting Borges don't really work), it does have a lot going for it. For the mass market, though, I think the issue is whether Rubinstein manages to find just the right balance between research and story, between exposition and narrative: even though a few times he does err a little too far towards the former, overall I think he earns enough goodwill from the latter to get away with it. Buy it, read it, enjoy it! :-)