Definitely a cut above the usual Dan Brownish genre novel. The Nostradamus stuff is important to the plot, but not overly-so. It's a reason for the plot to exist but not the be-all and end-all (the protagonists could have been chasing anything, really, be it a cache of diamonds or a phial of life-saving bacteria from the planet Zarg).
This is a thoroughly involving thriller, with characters who could actually be real, rather than stereotypes, with the exception of the Bad Guy, who's not in my opinion quite complex enough (he's a bit of a run of the mill psychopath, even with his Ancien Régime background). The gypsy stuff appears well-researched but not intrusively so; some authors insist on slinging in foreign words just to establish that they've really, REALLY researched their subject but Reading keeps a light hand, so the inclusions of Gypsy lore, language and customs don't appear to be bolted on.
The first part of the prologue, featuring a hanging, drawing and quartering, has little if any relevance to what follows, except to establish that our run of the mill psychopath had a psychopathic ancestor 450 years ago.
As another reviewer has commented, though, the Epilogue does appear to be a contrived way of justifying the book's title.
If you enjoy a good chase thriller in the Ludlum mould you'll enjoy this.