After his adventures with the mummies of Guanajuato and of being in the middle of the independence war, Leo San Juan is taken prisoner when he gets mistaken for an insurgent rebel by the royalist army soldiers while on his way back to Puebla. While locked in an old abandoned convent among other rebels, a frightening winged monster appears next to them: El Chupacabras, who attacks prisoners and guards alike. Abandoned to their fate, Leo and the rebels must fight the monster and escape before the royalists blow up the convent. As he struggles to survive he will discover the secret behind El Chupacabras and will have to make the most difficult decision of his life.