Spiral. Stuart Haydon Series, #3

"Scenes of homicide, Haydon thought as he stood over the reposing body, were contradictory affairs. The minimal constants, by definition, never varied: a criminal death; a Cain, an Abel. The variables were infinite: time, space, and circumstance. It was not when or where or why men murdered that made homicide investigations a tedious business. It was the surety of it, the inevitability that during every single day that dawned man could be depended upon to prove again that even after thousands of years of progressing civilization, he was utterly incapable of controlling his earliest criminal impulse.
In this one thing man was frighteningly consistent, and incorrigible."At the old abandoned Belgrano estate in a derelict section of the Latin barrio not far from the oil refineries and ship channel in Houston's east side, a neatly dressed dead man is found laying on his back in the wildly overgrown weeds behind the sagging wrought iron gates. In the very center of the man's lead colored forehead, just above his eyebrows, a single carpenter's nail protruded from his forehead.
There was no mess; it was very neatly done. One end of a tiny black string was tied to the nail, and to the other end of the string was tied a large red ant. The ant was trying to walk away from the string, and in doing so was clambering back and forth in a shallow arc across the dreaming gaze of the man's opened eyes. Thus opens the 3rd of five Stuart Haydon novels that plunges the wealthy, psychologically complex homicide detective into another encounter with the incomprehensible depths of human nature.
When the volatile mix of Mexico's social turmoil and unstable politics erupts into out-of-control violence, its devastating effects spill over its northern border into Texas. A well-financed, right-wing group known as Los Tecos, brings its vigilante justice to the streets of 1980s Houston during it's boomtown years, and Haydon quickly finds himself in the midst of a full-scale crusade of terror waged by a clandestine Mexican death squad.
Tragically the cross-fire of Los Tecos' murderous judgment claims the life of his longtime colleague and dear friend, and Haydon is swept into a  smoky world of conspiracy and political assassination. Soon he is engaged in a mortal struggle with a death squad "executioner" who proves to be a formidable adversary with an intellect and conviction equal to Haydon's. Sadly, real justice is hard to find in the mind spinning vortex of fanatical cruelty, and Haydon is tempted to give in to a dangerous paradox: to step outside the rule of law in order to enforce it.