In "Bloodline," documentarian Bruce Burgess explores the theory, made popular by Don Brown's recent bestseller "The Da Vinci Code," that Jesus and Mary Magdalene were lovers, that they fled to what is now modern-day France, and that French royalty can trace its lineage back to them and their children. The theory also posits that this "truth" has been carefully guarded by a shadowy organization called The Priory of Sion, and that the Catholic Church will literally stop at nothing to keep the story from getting out. Some contend that The Priory has been letting the details slip out little by little over the course of the centuries – mainly through art works with "coded messages" embedded in them - in a concerted effort to prepare the way for an illumination of the truth which, when finally revealed, will rock the very foundations of Christendom and thereby change the world.
Burgess spends much of the film interviewing people supposedly connected with or at least knowledgeable about the secret, individuals he meets in clandestine, off-the-beaten-path settings who speak in hushed tones about their theories and discoveries, and who claim to live in fear of their lives for even deigning to speak on the subject. The bulk of the second half of the film is taken up exploring what Burgess and amateur archaeologist Ben Hammott claim may be the tomb of Mary Magdalene, located in an isolated area in the south of France.
In all honesty, who knows what to make of this film or the conspiracy theory itself? Half the time the open-minded viewer feels as if he's watching something at least partway plausible – and the other half believing he's probably being made the dupe in an elaborate and colossal hoax. In fact, there are many sites dedicated to debunking the whole theory, including the entry on The Priory of Sion found on Wikipedia.
As a nonbeliever myself, I have to say that nothing put forth by this film strikes me as being any less plausible or historical than what is contained in the gospels themselves – which is to say that I find them both HIGHLY implausible and a-historical. I have no doubt that many people throughout the last two millennia have BELIEVED what Hammott and his minions are proposing, but that doesn't mean that any of it ever actually happened in real life.
Bloodline" is one of those movies that comes replete with a website where you can look up further information on the topic if so inclined. I suggest you look up quite a few others as well.