You may not have heard of the Maras. Or Barrio 18. Or the Jalisco New Generation Cartel, or the Zatas, or the Knights Templar, or the Shower Posse. But you should have heard about them, says Ioan Grillo in his new book about transnational drug and crime gangs, because any one of them may have played a profitable and blood-drenched role in bringing you not only your weekend baggie of recreational powder, but also the gold in your earring, the lime in your gin and tonic, the avocado in your salad and even the steel in your Volvo.