A replay is presented of a USS Victory away team recording from 40164.7 (five years ago) of the investigation of the disappearance of the Tarchanen III outpost personnel. The away Team includes Anthony Brevelle, Susanna Leitjen, Geordi LaForge, Hickman, and Mendez. The away team finds no sign of a fight, and the only evidence of the personnel is one tattered uniform.
On the modern-day Enterprise, Lt. Cmdr. Susanna Leitjen is briefing Picard, Riker and LaForge on the disappearance of the three other away team members. Over the past week, the three have left for Tarchanen III out of the blue, leaving Geordi and Leitjen as the only two people who have visited Tarchanen III and not gone missing.
The Enterprise heads out after Hickman who was spotted in a stolen shuttle craft. Geordi and Leitjen catch up in Ten Forward, and express their fears about the situation. The Enterprise catches up with the shuttle craft, with Hickman not responding to hails, continues on a direct course for Tarchanen III, destroying her shuttle when heading in too steep into the atmosphere. Upon detecting two more shuttles on the surface Picard sends Riker, LaForge, Data, Worf, and Leitjen to investigate. The away team finds the shuttles abandoned and split up to look around. Leitjen finds odd foot prints in the dust, Worf feels they are being watched, and LaForge finds a tattered uniform in one of the shuttles. When Leitjen doesn't answer her comm the others head out to look for her. LaForge finds her standing in the shadows, she is certain the others are alive saying "They're here, just stand still and listen, you can feel it they're here." Leitjen starts to walk away and fights LaForge when he tries to stop her. Geordi beams them up to sickbay.
Leitjen awakens in sickbay with Geordi by her bed side, Dr. Crusher tells her she had a histamine response (allergic reaction) but doesn't know what caused it. Leitjen wants to get back to the surface, claiming she wants to get back to work, but is ordered to rest, she settles for data analysis on board. Dr. Crusher reports to Picard that both Geordi and Leitjen are in perfect health. In the hallway Leitjen's hands start shaking and Geordi reassures her.
Data has discovered unknown alien skin cells on the torn uniform, and that the foot prints are not from any Tarchanen III lifeforms. Data runs a medical database search for the footprints and cells. Geordi and Leitjen look through both away team's records to find something that could cause people to want to return. Leitjen desperately wants to head down to the planet, and collapses. When Geordi runs over to her, he sees blue lines on her neck and her fingers fusing together,
Later in sick bay the blue lines cover all of her body, and her eyes are glowing yellow and very sensitive to light. Dr. Crusher tells Picard and LaForge that the people of Tarchanen III have mutated into another species, showing that Leitjen's cells and the cells from the uniform are the same. Crusher assures Picard that it is not contagious, but once started it can only be slowed down not stopped. Dr. Crusher tells LaForge that he will be next, in weeks or hours, and LaForge continues his investigation, with restrictions to prevent him from heading to the surface and regular visits to sickbay.
As Geordi gets frustrated with his lack of success, Leitjen begins mutating faster, emitting a scanner disruption field, and photo-mimetic abilities. Crusher tries to find a foreign body that might be causing the mutation. Geordi finds an extra shadow in one of the old away team recordings, as he enters the holodeck to investigate further, his hand starts to shake, just as he finds where the shadow caster was standing Geordi collapses, his hands mutated. Dr. Crusher finds a parasite causing the mutation and successfully removes it from Leitjen, but is unable to find Geordi to remove it from him. Geordi beams down to Tarchanen III, unable to scan for him the crew tries to figure out how to find him. Leitjen awakens and tells Dr. Crusher that the parasite is the alien's form of reproduction, Leitjen helps to find Geordi on the planet and convince him to return to the Enterprise due to her half-mutated state.
Geordi makes a full recovery and Picard has a warning beacon placed in orbit.