In this episode, the Holodeck fantasy life of a highly insecure crewman aboard the Federation starship USS Enterprise-D interferes with his ability to deal with malfunctions which threaten the ship.
The Enterprise is in the process of transporting Mikulak biological tissue samples intended for use in combating an epidemic of Correllium fever on Nahmi IV.
La Forge tells Riker he is concerned that one of his engineers, Reginald Barclay, has been underperforming and notes that he is late to help with the sample transport.
What La Forge does not recognise is that Barclay has been in the holodeck acting in a simulation of other Enterprise crew members, avoiding contact with their real counterparts.
They quickly narrow the field to two possibilities and determine that the one responsible for the system malfunctions is invidium, which had escaped from the leaking Mikulak sample container.
They are able to quickly repair the injectors, stop the ship, and set course for a nearby starbase to remove the rest of the invidium contamination.
According to episode writer Sally Caves, Reginald Barclay (Dwight Schultz) is a satirical depiction of Trekkies and their excessive obsession with imaginary characters.