Sight Unseen

Sight Unseen is the thirteenth episode of the sixth season of Stargate SG-1.

Plot
SG-1 comes back to Stargate Command with a strange device which was built by the Ancients. While they talk about the device Jonas suddenly sees a large, flying, insect-like being, which seems to fly through the wall. However no one else witnessed the wonder. Nevertheless, General Hammond orders the lockdown of the base even though searches turned up nothing, so Jonas' comrades think he might be having hallucinations.

While Col. O'Neill leaves the base to go fishing, Carter and Jonas examine the device. During their research, Jonas again sees a large insect and is immediately examined by Dr. Fraiser but they again find nothing out of the ordinary. Jonas is removed from duty. While talking with Teal'c, he sees another large insect, however, this time Teal'c sees it too.

Outside the base, O'Neill, while filling his car at a local gas station, sees an insect himself, pulls a gun, and shoots at it, much to the shock of the owner. He misses it and calls Gen. Hammond to report the incident, only to learn several people in the base have begun to see the creatures themselves. In the SGC, Jonas and Carter again study the Ancient device and discover that it allows people to see entities from another dimension, or as Carter calls it, "dimensional bleed-through." However, they are unable to ascertain how the machine affects people in this way, so they deactivate it, thus hoping to stop its effect. Later, Jonas and Carter talk with Teal'c in the cantina when a woman suddenly screams (apparently, she saw one of the insects). Because of this, SG-1 (without O'Neill) brings the device back to its home planet. The insects continue to appear, so SG-1 takes it back to Earth again. They conclude that the device not only attracts the insects, but allows them to see them by imparting a slight electrical charge which can then be passed from person to person. General Hammond quickly has Colorado Springs quarantined to stem the device's affect. Several military personnel are stationed in the nearby area, using a cover story of a hallucinogenic chemical spill.

For a third time, Jonas and Carter inspect the device and deduce that they have to rearrange the device's control crystals to produce the desired "antidote." Meanwhile, the owner of the gas station, which O'Neill visited earlier disbelieves the cover story and runs away, whilst the Colonel observes a car crash into the station's sign due to the driver seeing one of the bugs. Back at SGC, Carter and Jonas finally discover the correct crystal arrangement and begin to pass on the “cure” from person to person. However, the owner of the gas station, named Vernon Sharpe, eluding authorities, hitchhikes to the airport. In the meantime, Carter and Jonas find out more about Vernon through his local grandmother to narrow down where Vernon might be. She reveals that Vernon doubts the cover-story because of his prior experience in the Gulf War, where, he believed, the military experimented on the troops.

Vernon arrives at the airport and unsuccessfully tries to board a plane before the military cancels all flights and shuts down the airport. O'Neill drives to the airport in pursuit. Vernon, now scared out of his wits, hides himself in a nearby hangar. O'Neill locates the escapee and convinces him that he won't do anything to him. He also persuades Vernon that people will never believe his wild story of aliens from the planet Melmac. Vernon agrees to keep quiet and O'Neill cures him of the device's effects.