En route to Risa for a conference, Geordi is kidnapped by the Romulans and temporarily replaced with a doppelganger while the Romulans go to work torturing and brainwashing Geordi to turn him into an assassin. Let's start with the torture method: It's an ingenious story starting point. The Romulans use Geordi's visor inputs to tap directly into the visual centers of his brain; Geordi is forced to watch whatever horrifying images the Romulans feed him, and he's incapable of looking away. It's like A Clockwork Orange: The Romulans condition Geordi with images to psychologically break him. It's also like The Manchurian Candidate: Geordi is returned to the Enterprise with false memories, completely unaware he has been programmed as an unwitting sleeper agent.
Shortly thereafter, the Enterprise takes Klingon Ambassador Kell (Larry Dobkin) to a Klingon colony facing a rebellion. Vagh (Edward Wiley), the colony's garrison trying to quell the uprising, claims that the rebels are being armed with Federation weapons. Picard suspects Romulan involvement attempting to destabilize the region and drive a wedge between the Klingons and the Federation. That sounds about right for the Romulans. An investigation is launched. (TNG is always launching investigations.)
"The Mind's Eye" is more brawny, devious, and suspenseful than most TNG fare. It features a first-rate intrigue plot that grows from a general theme explored from "Sins of the Father" on to "Reunion," then here, and onward through "Redemption" — the notion of ongoing corruption in the Klingon Empire by conspirators in bed with the Romulans. There's even the establishment of a future major player (to be revealed in "Redemption") in the form of a silhouetted Romulan agent pulling the strings. The revelation that the Klingon conspirator is actually Ambassador Kell is skillfully pulled off (and I had forgotten the twist from my long-ago viewing of the episode). For a time it looks like Kell is a target when in fact he is the one triggering Geordi's mind-control instructions.
The episode works so well because it raises the stakes by making the would-be assassin one of our regular characters. The suspense builds through the last act as it becomes a race for Data to put together the pieces of the puzzle before Geordi carries out his assignment to kill Vagh. "The Mind's Eye" is effective, well-oiled, thriller-genre Trek.