Not many people know this obscure episode, because it was shot during the third season as an “extra,” to be used in a fourth season that never materialized. But here is the basic plot line. Kirk and the Enterprise visit a planet that, by mistake, received errant TV transmissions of “The Beverly Hillbillies” centuries ago. The inhabitants of that planet, being highly impressionable, have since organized their society along those principles and with Appalachian clothing, albeit with less couth manners. These creatures are mostly backward, but they have two special powers. First, neither Vulcan neck pinches nor phasers “set on stun” affect them, and second they have the ability to just walk through the otherwise protective shields of the Starship Enterprise.
In the episode, these “Penetrators,” upset at the backward state of affairs on their own planet, and encouraged by a nearby Klingon commander, attempt to take over the bridge of the Enterprise, using pipe bombs, chemical irritants, and Molotov cocktails, throwing one of the latter at Chekhov. Their motives are varied, but their manner is undeniably hostile and they arrive in a great swarm. Kirk issues orders to respond vigorously, and the intruders are stopped. This is, after all, the bridge of the Enterprise.
It is protected by a single, sliding door.
One member of Starfleet Command, an enemy of Kirk’s since they were classmates together at the Academy, attempts to have Kirk tried on charges of authorizing excess force against the Penetrators. But neither the Starfleet admirals nor the television audience side against Kirk. It was, after all, the bridge of the Enterprise that was being stormed. The Command also issues a statement recognizing the red-shirted Enterprise security guards for their (usual) valor in such extreme and perilous circumstances.
The Klingon commander escapes unscathed, though a well-aimed phaser shot cripples the communications ability of the Klingon ship.
Addendum: You won’t find this episode in the Star Trek DVD box, or on streaming, but recently they have put parts of it on TV. And here are my previous Star Trek posts.