IT IS SO BAD. Every chapter ends with a cliffhanger, and each chapter is only five minutes long in real time, but takes forever to read because no character can keep their head together for any period of time without "Chuck Vindaloo's memory drifted back to the last time he was in a car sitting on the back left seat". Half the time this is an "intriguing" flashback to something one of the main characters experienced as a little girl, which always veers off as it nears the climax, because he read somewhere that this is how you induce tension. The other half of the time it's a reference to his previous book which didn't sell for mysterious reasons (until this came out). The other other half of the time is just info-dumping about the Templars or Da Vinci or something else that would actually be interesting if it didn't stick out like a sore thumb (EG in Holy Blood, Holy Grail which to be fair they do name check).
I'd heard it was rubbish, but I was actually surprised at how comprehensively rubbish it was, how it went out of its way to sandbag any thrills and make the sandbags out of what would otherwise be interesting material. It's like a literary version of Speed, anytime it looks we might be getting a bit of pace, out comes the infodumping.