Great story - short but sweet. If it had been any longer, the ending probably would have become easier to predict, but as it was it came along at just the right time. I'm a sucker for myths like that, probably the result of growing up on Raiders Of The Lost Ark...
I think the Turin Shroud was proven to be a hoax, although it's a very old hoax which has led some people to speculate it's actually an early experiment in photography and the face is actually Leonardo DaVinci. DaVinci famously believed that John The Baptist was the true messiah, and this is why he painted himself into The Last Supper, with his back to Christ. You can also see a hand with a knife poised over Jesus' back.
There's also the theory that the Holy Grail is not the cup of Christ, but Christ's bloodline - his ancestors. The Bible skips from his boyhood to adulthood, leaving (I think) eighteen years unaccounted for. Legend has it that during this time Christ travelled the world and had a wife and family. His bloodline was Le Sang Royale (royal blood) which became corrupted into English as "Grail". Garth Ennis' "Preacher" uses some of this as the backdrop for much of the story.
Ripe territory for sci-fi and other fictional escapades, that's for sure.