Six secret operatives are the military's top experts in covert ops and rescue missions. But this elite special force doesn't exist - at least not in the public eye. No one knows where they come from or to where they return. The group gathers for the most dangerous, most difficult, and most important missions and often operates in extreme conditions. They are known only by their code name: Invisible Six.

When a deadly and highly contagious virus appears, Doc Dee and Invisible Six must find its source. The mission takes them deep into the Rift, a lawless section of the Amazon rain forest. But bandits and wild animals are the least of I-6's worries when the true enemy is invisible, widespread, and can't be beat by typical combat. Can Doc Dee and I-6 locate patient zero and stop a pandemic from happening?