The problem with films based on 'real' conspiracies is their unwillingness to fit a three-act structure. You end up either expanding the facts - which negates the point - or producing something with clunky cinematic gaps whenever you pass the limits of the definite. Here, there's no doubt writer/director Urban knows his stuff; he just fails to transfer it to the screen.
For example, at one point, characters suddenly decide to go from Rennes-le-Chateau in France, to the Greek island of Patmos: why is not explained. It's all part of the hunt for the Loculus, a box connected directly to Jesus Christ, which billionaire Magnus Martel (Terence Stamp) finds - but having seen its potential, deliberately loses. He is rapidly killed by a Mason-esque order, under Grand Master Udo. It's now up to Martel's son (D'Arcy) and a conveniently handy alchemist (Wightman), to track it down before the Grand Master does.
Things get going once the Loculus is found, with its role a genuine surprise (a clue: it's actually empty!). The fate of the characters is unexpected as well, even if the movie begs a sequel that now seems unlikely. But it's as if they wrote the end first, with no idea how to get there, and the machinations required are what hurts: if Martel really wanted to derail the Grand Master, all he needs is a furnace. The documentary on the DVD about Rennes-le-Chateau, hosted by Lionel Fanthorpe, cheerfully admits ignorance where necessary - and as a result is more effective than the film.