 Trip and Hoshi are returning from a visit to a planet where the Klingons once landed. Nothing interesting could be found, but in the shuttle pod back Trip suddenly starts coughing. A while later he collapses. Dr. Phlox finds out they are infected by a silicon-based virus. He estimates that the pathogen will kill them in five hours. Meanwhile an alien species seems to have taken over Mayweather and Reed. They are discussing the behavior of the Humans. For 10000 years they have been observing the reactions to the viruses to measure the intelligence of the infected species. Will the crew surprise them?