While scuba diving in Tanzania, Sam and Remi Fargo come upon a relic belonging to a long-lost Confederate ship. An anomaly about the relic sets them off chasing a mystery, but unknown to them, a much more powerful force is engaged in the same chase. Mexico's ruling party, the ultranationalist Mexica Tenochca, is intent on finding that artifact as well, because it contains a secret that could destroy the party utterly.