Pedro de Vargas is a young 16th-century Spanish nobleman accused of heresy by the inquisitor Diego de Silva. After his 12-year-old sister is tortured to death, friends help him and his parents to escape. Vargas sees his parents safely out of Spain and enlists in Cortes' army, on its way to the New World in search of riches and fame, until he can avenge his sister's death. He rises to the rank of captain, but De Silva arrives during the march to Mexico to unmask the heretics in their ranks.