First Contact: ‘Identity Crisis’ Season 4 Episode 18

Geordi’s former colleague Lieutenant Commander Susanna Leijten comes on board. She’s worried that all of their former colleagues from a mission to Tarchannen III have deserted Starfleet and disappeared. She begins to act increasingly strangely and wants to go down to the planet’s surface before she begins to transform into a strange alien creature. Doctor Crusher investigates the medical possibilities while Geordi goes over old logs searching for a clue. It turns out aliens plant their DNA in visitors in order to reproduce, which seems challenging when you think about it.  Crusher discovers a way to reverse the process, but will it be too late for Geordi? 

Listen to the previous episode ‘Night Terrors’ here