The Enterprise is called into the Neutral Zone to help a fellow Galaxy-class ship, the USS Yamato, which is in the grip of a series of system malfunctions. They arrive Late to the Tragedy and Rocks Fall, Everyone Dies. Oh, and the Romulans appear to deny everything.
Interestingly, Geordi confirms that the Romulans weren't responsible for the Yamato's destruction, but Picard isn't convinced, and after a thorough study of the ship's logs, determines its previous mission: its captain was leading his crew on a wild goose chase for Iconia, one of a bajillion mythological planets out in the Trek universe, and he thought to have found it on the Romulan side of the Neutral Zone, where they met... something... that seemed to have caused their system failures. Since Iconia is said to have insanely powerful technology that the Romulans could use to crush the Federation, Picard sets course to the planet the other ship's captain believed was the fabled planet.
Unfortunately, the Enterprise starts coming down with its own set of systems failures, which Data and Geordi fail to solve or determine the cause of (possibly because Data is acting way Out of Character). Once they get to what is believed to be Iconia, a probe is launched from the planet's surface, which Geordi—finally realizing what's going on by that time—convinces Picard to destroy before it has a chance to do anything. By his calculations, the probe contained an Iconian computer program that transferred itself into the Yamato's systems when it visited the planet, and transferred itself into the Enterprise with the ship's logs, and which is attempting to rewrite all of the Enterprise's software in its own image; unfortunately, since Starfleet doesn't have so much as Norton Antivirus to fend off what's essentially a Trojan horse virus, there's no way for them to fix the problem.
Running out of options, Picard takes Data and Worf down to the surface, into an underground installation discovered by the ship's sensors, and proceeds to scout around, looking for anything they can use to determine the origin of or a means to destroy the program. What they discover is something more complex and sinister; an ancient transport union ripping open holes in the space-time continuum to travel through, thus earning the Iconians' nickname of "Demons of Air and Darkness" by their enemies. Picard is convinced this violation of physics was used for peaceful purposes only (yeah, right), but can see how it could be used as a weapon by the Romulans, who conveniently show up to harass the Enterprise and lay claim on the planet. Fortunately for all involved, aside from the Romulans, the Romulan ship has come down with the Iconian computer flu as well, preventing them from acting on their threats.
Unfortunately, however, Data becomes infected with the virus as well, and is forced to be taken back to the Enterprise for repairs, but not without informing Picard on how to destroy the compound and the technology within. The episode ends with Picard managing to use the rip in space and time to escape onto the Romulan ship (stuck on auto-destruct, at this point) before being beamed off, and Geordi showing we will not use system restore in the future by forgetting he could reboot and purge the ship's computer core after Data does the same to his systems, sharing the solution with the Romulans (who don't know how to use it, either) before spiriting off.
This episode contains the following tropes:
- Blind Jump: Played with. Picard sets the gateway console to explode, planning to use the gateway to escape. Even if he can't get to Enterprise, which the gateway will cycle to eventually, wherever he ends up it'll be better than being blown up. Fortunately, the gateway cycles to the nearby Romulan ship, which Picard figures is better than nothing. By this point, the Romulans have computer failure so bad that their ship is going to blow itself up and the captain doesn't feel shooting Picard is even worth the effort. He's beamed off when Enterprise detects his signal.
- Butt-Monkey: Geordi gets thrown around in a turbolift, gets electrocuted, and completely fails to recognize the easy solution to the Enterprise's problems until Data gets infected and then fixes himself.
- Chekhov's Gun: In his Captain's Log, Varley mentions being scanned by an Iconian probe. This turns out to be the cause of his ship's malfunctions, as well as those on the Enterprise.
- Clarke's Third Law:
- Wesley references this trope during his conversation with Picard when he says the ancient Iconian's technology sounds more like magic.
- Captain Varley of the Yamato compares encountering the Iconian technology to a caveman confronted by a tricorder.
- Contagious A.I.: The Iconian probes scan ships and try to reprogram them with Iconian software, possibly by complete accident. Unfortunately, said ships tend to get very explodey when the alien software overwrites the programs that keep things like the antimatter fuel safely contained in magnetic fields...
- Drink Order: This episode marks the first time Picard orders "Tea, Earl Grey, hot." Unfortunately, the Enterprise's computer is so messed up it gives him a potted plant instead.
- Failsafe Failure: The Yamato's warp core breached because the computer dropped the antimatter containment field prior to all the antimatter being ejected.
- Have You Tried Rebooting?: After Data's "self-correcting program" resets him, Geordi reasons they can do the same thing with the Enterprise computers to wipe out the Iconian programming.
- It Never Gets Any Easier: When Wesley has trouble accepting the deaths of everyone on the Yamato, Picard tells him that it's no less painful for senior officers.
- Morton's Fork: Riker isn't keen on Geordi's plan, since it involves turning everything off including the deflector shields while they're "nose-to-nose with a Romulan Warbird." Geordi points out whether it's Romulan disruptors or their own warp engines, they're just as dead if they don't do this.
- Names to Run Away from Really Fast: The Iconians' nickname of "Demons of Air and Darkness". Though Picard does put forth the theory that they were only called that because their technology appeared to be magic to those they interacted with, and those species were frightened enough to attempt to destroy the Iconians.
- Rousseau Was Right: When an Iconian probe heads for the Romulan ship, the Enterprise has lost its weapons and can't destroy it, so the fate of the Romulans rests on whether they trust Riker when he says that they need to destroy the probe themselves. Though very suspicious, they decide to trust him and destroy the probe, saving themselves.
- Self-Destruct Mechanism: Picard finagles one to destroy the gateway, by launching all of the probes and forcing the launch bay doors to channel the rocket exhaust into the gate room. The Romulans have to deal with theirs being triggered (and then locked) by the Iconian Trojan horse.
- Thrown Out the Airlock: Varley mentions that he lost an entire maintenance team when the force field in the open shuttle bay they were working in shut off.
- Unusual User Interface: The Iconian console, which processes commands based on tapping different coloured portions of a logo.
- Written by the Winners: Picard mentions this when he figures that the warlike depiction of the Iconians may have been wrong, passed down by those who feared and eventually defeated them.
- The Worf Effect: The USS Yamato, a starship of identical build and design to the Enterprise, being destroyed (complete with the saucer separating and then disintegrating in front of the main characters!), is meant to show us and the crew that the Iconian computer virus is serious business.