In a hidden cave in the mountains of Lebanon, a man makes a fateful discovery. He has been chosen to be the carrier, to bring what has been forbidden for thousands of years out of the darkness and into the light: the Testament of Lucifer.

In Istanbul, Bravo Shaw, head of the Gnostic Observatine sect, has been warned by his ageless confessor, Fra Leoni, of a battle most ancient: the war between Good and Evil, waged to a standstill since time immemorial. Now something has altered the balance of the power. An unfathomable danger has arisen: Lucifer's advance guard, the Fallen. All of humankind is in imminent danger of being enslaved by the forces of evil. Bravo, Fra Leoni, and Bravo's blind, brilliant sister, Emma, are the first and last line of defense against the chaos unleashed by the Testament of Lucifer.

But without the help of Ayla Tusik they will fail. When Ayla's parents, Turkish friends of Bravo's, are cruelly murdered, Ayla must decide to help or hinder them. Who is she really? More to the point, what is she? Bravo will have to unravel that puzzle if he is to have any chance of holding the line against the high minions of the devil. All roads lead to the Book of Deathly Things: the Testament of Lucifer. But if he and Emma become privy to its dreadful secrets they very might well forfeit far more than just their lives.