Neil Johns has just started his dream job as a code breaker in the NSA when his brother, Paul, a mycologist, goes missing on a trip to collect samples in the Amazon jungle. Paul returns with a gap in his memory and a fungal infection that almost kills him. But once he recuperates, he has enhanced communication, memory, and pattern recognition. Meanwhile, something is happening in South America; others, like Paul, have also fallen ill and recovered with abilities they didn't have before.
But that's not the only pattern - the survivors, from entire remote Brazilian tribes to American tourists, all seem to be working toward a common, and deadly, goal. Neil soon uncovers a secret and unexplained alliance between governments that have traditionally been enemies. Meanwhile Paul becomes increasingly secretive and erratic.
Paul sees the fungus as the next stage of human evolution, while Neil is convinced that it is driving its human hosts to destruction. Brother must oppose brother on an increasingly fraught international stage, with the stakes: the free will of every human on earth. Can humanity use this force for good, or are we becoming the pawns of an utterly alien intelligence?