David returns to Mexico to find Carlos and to deal with the drug-resistant TB strain that has been killing the Zapatista rebels Mayko and Rachel get a lead in the mysterious outbreak in Hudson and Bob comes out of a medically-induced coma with little memory of what happened to him.

Bob is haunted by memories of his time at Roth's secret lab; Wes insists that Rachel inject him with a highly experimental decoy drug to fight the virulent Hepatitis C. A contagious disease appears in a small town, resulting in mysterious brain inflammation.