Observer Effect

Two non-corporeal aliens take over the bodies of Enterprise crew members, one after another, to study how humans behave in a crisis. Their test arrives when Tucker and Hoshi return from a planet survey infected with a deadly silicon-based virus. As Phlox battles to save them, the observers disagree: the elder insists on strict non-interference, while the younger is troubled by the suffering they are watching. Despite every effort, Tucker and Hoshi die, and then Archer is infected too. Archer confronts the watchers and condemns their cold detachment. Moved by his argument, the younger alien persuades the elder to intervene. They revive and cure all three humans, erase the crew's memories of the encounter and leave. The aliens are revealed as Organians, who have spent centuries judging spacefaring species and now decide to make proper contact with humanity a century later.