Quammen is a good storyteller here as in other books. He leads readers through the process of studying the source of the AIDS virus, surprisingly finding the spillover happened in 1908. He travels to the area where the spillover happened and the concentration of HIV was greatest and creates a possible scenario for the spread downriver to Leopoldville, another site of many occurrences. He reminds readers frequently that this is educated guess. It provides an interesting change from the reporting of the scientific work. When he speaks of the research he speaks more authoritatively--still letting the reader know when a finding is sure and when it is speculation. Because he is following the trail of discovery, what is "sure" sometimes changes with additional study.

A fascinating read, as engaging as any mystery.