While Dan Brown saw significance in the letter formations created in the fresco -- the perfect W created by Jesus at the centre, for one -- Sierra plumbs a hidden phrase from the letters of the Apostles names and their positions on the mural.
Leonardo is an enigma himself, always dressed in white like Apostle Simon and living a secretive life with a stable of young apprentices. He refuses to eat meat and is said to practice celibacy (except, as the author points out, he "fancied men -- which would make him not as celibate as some assert").
While waiting for inspiration, Leonardo is said to have worked slavishly on his inventions, mostly of a labour-saving nature but whose success was often determined by the number of fatalities they caused. To keep his notes from prying eyes, he wrote backwards using a mirror.
What Sierra reads into The Last Supper is that Leonardo was a Cathar, a sect that practised abstinence from food and sex to purify themselves but which was thought to have been exterminated during the Crusades in Southern France in 1244. Also factored into this story is a mysterious blue book owned by Leonardo, one said to have recorded a discussion between Saint John and Jesus in heaven.
The ancient Oriental treatise, the death of many in Sierra's story, is called Interrogatio Johannis, or The Secret Supper. It was purportedly the bible of a new church, one that would fly in the face of Catholicism. Were its contents encoded in Da Vinci's mural?
From a European standpoint, The Secret Supper is, like Da Vinci's fresco, a masterpiece -- the most talked about book of the year -- from an already popular Costa del Sol author who cut his teeth on a series of earlier historical enigmas, including one about the secretive Templar sect.
Rights to the novel have been sold in 25 countries and its release 10 days ago was accompanied by a no-holds-barred, Da Vinci Code-style marketing campaign.
Unlike Brown's epic tale, Sierra keeps you guessing to the bitter end -- the last line on the last page of the book's last chapter, in fact. What Sierra has produced is more than just a clever, spine-tingling mystery but a great divide -- those who will swear by Brown and those who put Sierra to the head of the Da Vinci class.
In truth, Sierra's story -- soon to face The Da Vinci Code's heavy Hollywood guns -- is more than just a contender. It leaves Brown's fabled tale in the dust.
Be warmed though: If you don't thoroughly enjoy The Last Supper, there's no dessert.
You can find the review here