On the border of the United States and Mexico, a war is raging that can never be won by conventional means. The drug cartels are rampant. Their victims number in the tens of thousands. Men, women and children are butchered in the most obscene ways imaginable. Of all the cartels, the most violent is Los Zetas. Made up of former Mexican special forces turned bad, they are perhaps the most ruthless and highly trained criminals in the world. Which is why only the most ruthless and highly trained operatives can ever hope to be a match for them. Enter the Regiment. When the CIA reaches out to the British military for help, SAS legend Danny Black and his team are despatched to give the Zetas a taste of their own medicine. Working deniably and under the radar, their mission is to bring death and mayhem to the cartel, and to coax out into the open their elusive leader, the iconic Z1. But, the arm of the cartel is long, their strategies underhand and brutal. And in the dog eat dog world of this clandestine war, nothing is ever quite as it seems. It will take all the SAS team's skill to break through to the heart of the cartel. And even they do not know what they will find ...