The Devil's Elixir by Raymond Khoury

Sean Reilly and Tess Chaykin, heroes of Raymond Khoury's bestselling Templar thrillers, return in an edge-of-your-seat story that reaches from the present day back to 1800s Mexico-and possibly beyond. What if there was an herb, previously lost to history in the jungles of Central America, capable of inducing an experience so momentous it might shake the very foundations of Western civilization? What if powerful forces on both sides of the law got wind of that herb, and launched a violent, uncompromising pursuit to be the first to exploit it? And what if FBI agent Sean Reilly and his girlfriend, Tess Chaykin, were, unknowingly, the only two people who could keep the lid on this existential Pandora's box, one that's capable of destabilizing the world?