This is the fourth book in this series of genre mash-ups, combining cops, criminals, vampires and the supernatural. The book in the title refers to a real, historical document: The Florentine Codex. It is fantastic adventure, through and through. Swordplay, gunfire and explosions galore. A spectacular melange of battles and more than a tinge of romance. The Florentine Codex is an ethnographic document cataloguing the Aztec civilization after the conquest of Mexico by Hernan Cortez. 12 volumes long, it was the life's work of Bernardino de Sahugun. When Bernardino died in 1590 the book was lost in Florence's Laurentian Library for 199 years. Upon its rediscovery the book became an absolute sensation among academics, particularly students and professors in Mexico who wanted to learn about the civilization that once ruled their country In 1835 a student, Don Fernando, suspects that a Thirteenth Book was stolen containing the secret location of an Aztec treasure more vast than the Spaniards had ever dreamed of. He comes under the thrall of Victor Orloff who will have a fateful influence on him. Fast-forward to the present day abduction of an immortal: Falco's mate, Diva, who is the target of an unbelievably loathsome plot. Seduced and bewitched with magic potions she descends into primal depravity. Diva may be lost to Falco forever. Falco discovers that Diva has been spirited to the State of Veracruz and finds himself in the midst of a war between two rival Mexican cartels, which are trying to destroy each other. One cartel is led by Ernesto Dominguez who has an impregnable fortress in the city of Veracruz. The other cartel is led by Carlos Heredia whose Rancho de la Cielo Azul is guarded by a small army. The two cartels ruthlessly attack each other, attempt to hijack drug shipments and murder each other. Spies infiltrate each camp in the attempt to gain the upper hand over the other. The Zetas, rogue ex-Mexican Special Forces, act as a wild card between the warring cartels. They have developed an antipathy for the humble people of the town of Ambrosita who have risen up to resist them. There are corrupt army officers, a corrupt mayor and corrupt police. Falco will have his hands full. There are homeless people who have been hired to assist an archaeological expedition in Pico de Orizaba, the highest mountain in Mexico. All the while the Woman of Sorrow lurks in the shadows. There are heroic soldiers and vigilantes who form an alliance to try to destroy their enemies. There is an ancient uspeakable evil that must be destroyed. There is a treasure beyond imagination to be discovered. A hero is needed to tip the scales to favor the righteous. It is Falco, the Dark Angel.