Based on her examination of Susanna, Dr. Crusher determines that the people who disappeared from Tarchannen III were not abducted, but transformed into another species. While Beverly searches for the cause of Susanna's transformation, Picard issues an order that Geordi's every move be monitored by computer in case he should also be motivated to leave the ship. Geordi spends his time aboard ship painstakingly reviewing a visual recording made five years ago at the scene of the original investigation.

While reviewing the tape, Geordi notices a shadow that has no known origin. He recreates the entire scene in the Holodeck, determining that an unknown creature was present on the planet during the fateful Away Team mission. Moments later he is struck with a sudden pain, and looks down to see that his two middle fingers have fused together. Meanwhile, Dr. Crusher locates and removes the parasite responsible for Susanna's transformation. Hoping to scan Geordi for the parasite before it affects him, Dr. Crusher summons Geordi, but a security team discovers his torn uniform and sees a half-alien Geordi overcome a transporter technician and beam to Tarchannen III. Susanna insists on accompanying the Away Team on their search for Geordi, insisting that what she has gone through will help her find him. She is allowed to go, and finds him almost completely transformed. However, she is able to appeal to his human side and talk him into returning to the starship, where he undergoes surgery and regains his human identity.