Ep 11. Observer Effect

In Season 4 Episode 11 of Star Trek: Enterprise, titled Observer Effect, the crew of the Enterprise encounters a group of disembodied alien beings known as the "Organians". The Organians are able to exist in a state of pure energy and can manipulate matter and biological organisms. They have been studying the crew of the Enterprise and decide to conduct an experiment by taking over the bodies of two crew members, Ensign Mayweather and Lieutenant Reed.

The Organians take over the bodies of these crew members and begin to conduct their own experiments on the ship while the crew is unaware of their presence. These experiments include testing the crew's ability to detect the Organians and observing how they react to different scenarios and situations on the ship.

During their time in the bodies ofcrew members, the Organians begin to experience emotions and begin to question the morality of their experiment. They start to feel empathy for the crew members and realize the impact their actions could have on the ship and its crew.

Meanwhile, the crew of the Enterprise is dealing with a crisis involving a deadly virus that is spreading rapidly throughout the ship. The virus is so deadly that it kills any crew member who contracts it within a matter of hours. The Enterprise is in danger of losing many of its crew members if a cure cannot be found soon.

As the Organians continue to conduct their experiments and struggle with their newfound emotions and moral conflicts, they begin to see the virus outbreak as an opportunity to test the crew's ability to overcome a crisis and work together to find a solution.

The crew, unaware of the Organians' presence, work feverishly to find a cure for the virus before it spreads further and kills more of their fellow crew members. Despite facing numerous obstacles and setbacks along the way, the crew manages to work together and eventually finds a cure, saving the lives of many of their crew members.

In the end, the Organians make the decision to leave the bodies of the crew members and return to their own state of pure energy. They realize that their experiment may have had unintended consequences and vow to never interfere with the lives of biological organisms again.

The episode ends with the crew of the Enterprise reflecting on their experience with the virus outbreak and their ability to overcome a crisis together as a team. They are unaware of the Organians' presence and the role they played in the events that unfolded.