Identity Crisis (Star Trek: The Next Generation)

"Identity Crisis" is the thirteenth episode of the fourth season of the American science fiction television series Star Trek: The Next Generation. It first aired on January 28, 1991.

The episode centers on Lieutenant Commander Data and Lieutenant (junior grade) Geordi La Forge investigating a strange phenomenon occurring on the planet Tarchannen III, a planet where La Forge previously served during a Starfleet away mission several years prior. During that mission, several members of the landing party vanished without a trace. Data and La Forge discover that the missing crew members are being transformed into a primitive, non-humanoid lifeform through a unique retroviral infection.

Dr. Crusher's investigation reveals that the virus rewrites the host's DNA, causing a slow and irreversible metamorphosis into the alien creature. The transformation is triggered by exposure to a specific wavelength of light found on Tarchannen III. La Forge himself begins to exhibit symptoms, experiencing flashbacks and visual distortions, indicating that he was infected during his initial tour of duty.

The episode explores themes of identity, transformation, and the fear of the unknown. The crew of the Enterprise struggles to understand and reverse the process while facing the possibility of La Forge losing his humanity. Ultimately, Dr. Crusher is able to synthesize an antibody that halts the progression of the retrovirus, saving La Forge and potentially others who may be infected. The episode concludes with the understanding that the native creatures were once humanoid and were also victims of this transformation, highlighting the tragedy of the situation.