Tex goes to El Morisco to reunite with his son Kit and his Navajo friend Kinlay, but in a hostile Pilares the Ranger discovers that the elusive Jaguar Men have attacked and set fire to the scholar's house, killing the Indian. The "brujo", Eusebio and Little Hawk have vanished into thin air!
At night, among the ruins of El Morisco's house, destroyed by phantom beings, Tex meets Eusebio, the scholar's assistant. El Morisco, taking refuge in a cave, tells the Ranger about the assault of the Jaguar Men, led by a fanatic masked as Tezcalipoca, a sinister Aztec deity! The madman had stolen a precious pre-Columbian code from the brujo and kidnapped Kit Willer. Since part of the manuscript is preserved in the San Diego mission, Tex and Morisco set off to anticipate the assassins' moves, discovering that they have massacred a military outpost along their path.
Intercepted by Mexican soldiers furious at the massacres, Tex and Morisco are incarcerated in Casas Grandes. When they manage to escape, Montales arrives to get them out of trouble! One of Tezcalipoca's Jaguar Men, captured during the assault on the city barracks, has freed himself: at the end of a bloody battle, the monster is killed and the feline spots that covered him vanish as if by magic! Tex and the Morisco decide to go to the San Diego mission to find the missing part of the Aztec code stolen by Tezcalipoca, before the human beasts get there!
The San Diego mission guarded by the moody Father Xavier hides evidence of ancient technologies and alien landings. And while El Morisco studies the newfound part of the Aztec code, the Jaguar Men attack! Once the fighting is over, one of Montales' soldiers recognizes his cousin from Valle de Rosario in the body of one of the monsters. Our team thus follows the new lead, after witnessing the madness of Father Xavier, who blows up the mission with all its secrets! Once they reach their destination, Tex and the others find an ally in Antonio Herrera, owner of the surrounding mines.
In Valle de Rosario, guest of the Herrera brothers, El Morisco is attacked by Tezcalipoca and the Jaguar Men to steal the missing part of the pre-Columbian code. A heavy climate of silence weighs on the town and a church, in which the youngest members of the pueblo disappear in droves, conceals the passage to an underground Aztec temple. Here, where the vapors of a mephitic pool transform those who immerse themselves in it into human beasts, the fanatic Tezcalipoca harangues a hallucinated crowd of campesinos, promising the rebirth of the ancient gods, whose favor is to be propitiated with the sacrifice of Kit Willer!
Tex and Montales save Kit Willer just when Tezcalipoca's knife is about to sink into his chest! Having overcome the barrier of the Jaguar Men, our men reunite with Antonio Herrera, while El Morisco, in the villa of the rich Mexican brothers, discovers the true face of the enemy! The goal of Tezcalipoca and his fanatical and beastlike followers was to resurrect the most ancient soul of those lands, in a new Aztec nation, armed with a powerful explosive whose secret was noted in the pre-Columbian code. Dreams of glory soon destined to shatter.
