The story is told in Agostino Leyre's words, as mysterious letters come in to Rome.
He is a chief inquisitor, and so he decides to investigate who had sent these mysterious letters, hinting at heresy.
He goes to Santa Maria delle Grazie, where he meets various monks, priests and nuns.
But while he is there, various suspicious deaths and rumours takes him into a search for truth- the meaning of The Last Supper.
Intrigued, he finds yet another mystery - a blue leather-bound book, portrayed in tarot cards left by the killer of several pilgrims, known as 'The Soothsayer'.