At the end of 1899, in Mexican state of Sonora, National Rural Policeman Miguel Ángel Ibarra, recovering from a small stroke that has changed his view of the world, begins to think that the rights described in the Mexican Constitution of 1857 should apply to the Yaqui Indians as well, whom, first Spanish, then Mexican governments had been trying to wipe out for hundreds of years. This new conviction makes him the enemy of state and federal forces and gets him into desperate situations, as he tries to solve a robbery committed against an American-run mine in the Bacatete Moutains east of Guaymas. There he stumbles onto a dark secret, where he comes into direct contact with the plight of Yaqui miners.