The incorrupt body of Venerable María de Jesús de Ágreda in the Church of the Conceptionists Convent (in Ágreda, Spain). Photo taken from Maria de Jesus de Agreda's Wikipedia page.
Javier Sierra is probably one of the more successful authors, world-wide, who you've never heard of. I've only read two of his works; they may be the only two of his translated into English. They're reviewed below.
The Secret Supper
No Da Vinci Code redux, as a commenter inside says, and it's true. Very good book about everything associated to its time. A bestseller in 35 countries, this book delves into the characters more than Code, with just as much suspense and with just as many cliffhangers. And the added bonus of historical accuracy and a You-Are-There feel. Sierra has yet to repeat this success, unlike Brown and Angels and Demons (which might be better than Code). This is a worthwhile book and intelligent escapism.
The Lady in Blue
Disappointing, but not terrible. Made me want to see images of the nun who, though in her crypt, still looks alive. Very, very creepy. Interesting question about how the true Americans knew the religion beforehand, though I can think of other, more plausible, answers. Very second-rate compared to Sierra's own The Secret Supper, and sometimes kinda bland. He'll do better. Very successful book, translated into 23 languages, as was The Secret Supper.