"Siege in Superspace"
The Enterprise is underway to Draconis, a semi-civilized planet seeking admission to the Federation, to report on their social and cultural conditions. Mr. Spock reports a malfunction in the "pressure gauge." "Impossible, Mr. Spock!" Kirk says, "All our systems are programmed for self-repair!" Spock tells the Captain that it will not take long to make repairs, however the engines will have to be shut down. He recommends placing the Enterprise in orbit around something first. Sensors report the neutron star Nymyn is "14 marks northwest", and Spock orders Scotty to cut power to the engines as they enter orbit around it.
As Scotty is making repairs, he notices a problem. "Captain," he says, "either something is wrong with our instruments, or that star has suddenly begun to radiate vast quantums of energy!" "Both, Mr. Scott!" Spock says, "The energy is overloading our computer systems, causing them to malfunction!" "Where is the energy coming from?" Kirk asks. "Have you ever heard of a 'black hole', Captain?" Spock replies. "I'm afraid not, Mr. Spock!" says Kirk, "Please explain!" "(It is impossible that a starship captain has never heard of a black hole) You see Captain" the Vulcan continues, "Gravitational pull continues even after a star has burned itself out. Eventually, the dead star's mass simply collapses into oblivion. My guess is that Nymyn is about to undergo gravitational collapse!"
The Enterprise exits the black hole, and enters orbit around a large planet. "Any guesses as to where we are?" asks Kirk. "Yes Captain" Spock replies, "I believe it is called 'superspace', the all encompassing entity which exists beyond our own infinite universe!" While Scotty and Spock begin making repairs, Kirk beams down to the planet surface along with Dr. McCoy and Lt. Uhura.
The landing party discovers lush plant life on the planet. As they look around, they see a young woman in a purple uniform fleeing from a huge creature made of vegetation! "I don't know who you are or where you came from" she cries, "but help!" Kirk and McCoy attack the creature with their phasers. They fire repeatedly, and are finally able to bring the monster down as their phasers weaken.
"I am called Rhuna" the woman says. "My home is Caeminon, the kingdom beneath our world's surface!" "I certainly hope it's safer down there" McCoy quips. "It's much safer, my friend" Rhuna replies. "That's why my people were forced to migrate down there centuries ago. We were once a proud and mighty civilization here on the surface. Then our scientists created the ultimate defense weapon to insure peace among the citadels. The weapon was activated when alien invaders besieged our planet! Then the machine went out of control, indiscriminately destroying everything in sight! We were fools to think we could win peace by creating the strongest weapon! This is what we have wrought. As life on the surface became extinct, the machine hibernated for several centuries. Then our monitors recorded the landing of a galactic space patrol vehicle. When the machine's sensors detected another human presence, it reactivated itself. His craft destroyed, the pilot had no hope of escaping our planet alive. But in fleeing from the machine, he discovered the nuclear reactor which once supplied our world's power."
"Realizing he was doomed anyway, he set the energy controls far beyond the danger level and set off a nuclear holocaust, killing both him and the machine. We can only guess what happened next, but we suspect that the 'Mind Module' which controlled the machine somehow survived. Since the mind-module had been programmed for self-survival, it protected itself by genetically altering the vegetation to create an army of vegetable creatures like the one we encountered earlier. We sent up expeditionary forces to the surface, hoping it could again be made livable. I was among them. But our party was attacked by those plant creatures. Only I survived."
Rhuna tells them that her lover had given his life to save hers in the attack. As he was dying, he gave her a bracelet of colored glass and stones that he had found. "That was barely an hour ago" Rhuna finishes, "and you know the rest!" Rhuna leads the landing party to a secret tunnel nearby, and then underground - to a magnificent city in a cavern. "We have arrived, Captain!" she says. "Welcome to Caeminon!" Meanwhile, on the Enterprise, Spock and Scotty continue to work on the repairs. "And a lot of good it'll do us, laddie!" the Engineer says. "How do we get back to our own universe?" "I don't know, Mr. Scott" Spock answers, "I honestly don't know!"
Rhuna introduces the landing party to Anthar, the Governor of Caeminon. Anthar welcomes them and asks Kirk how they arrived on the planet, and how they had managed to survive the attack from the plant creatures.
The plant creatures begin ruthlessly killing the city dwellers, even though they try to fight back valiantly. "Captain" McCoy says, "The citizens are being slaughtered! We've got to do something!" Kirk asks Rhuna if there is anything that can be used against the creatures. "There are energy pools along the outskirts of the city" she replies. "Normally they provide our power source, but if we could lure the creatures near them..." She and Kirk quickly set off to the pools, luring some of the creatures to follow them. They leap from rock to rock across the pools, however the plant creatures stop at the edge and will not follow them. One of the creatures fires an energy beam that starts a rock slide. Kirk and Rhuna narrowly escape death! "I think we underestimated the intelligence of those plants!" Kirk says. "I suspect the only real way to defeat them is to find the Mind Module controlling them, but we have no idea what it looks like!"
Meanwhile, the Doctor and Lt. Uhura continue to fight the creatures with the citizens of Caeminon. Uhura is thrown off balance by an energy blast, and twists her ankle. A plant creature approaches her, and McCoy saves her in the nick of time by killing the creature with his phaser. "Those last minute rescues are bad for my nerves!" she says.
Rhuna leads Kirk to an old warehouse, where Caeminon's weapons were stored after they had been outlawed in the city. Kirk uses his phaser to blast the door open, and inside they discover everything from swords to laser weapons. At that moment, Spock calls the Captain from the Enterprise. "I bring you good news!" he says, "Our sensors show that a nearby star is likely to go nova within six hours! Do you realize the implications, Captain?" "Certainly, Mr. Spock" Kirk replies. "If we can employ the energy discharged by the nova, maybe we can generate enough energy to get us back to our own universe!" Just then, several plant creatures break into the warehouse. Kirk kills one with a sword, and Rhuna uses a laser rifle on the other. "Odd!" Kirk says, "The nearer those creatures are to Rhuna, the more her bracelet glows! Wait - that's it!"
"Your people have nothing more to fear" Kirk says to Rhuna, "I have an idea how the Mind Module can help us! I'll order Mr. Spock to beam us back to the Enterprise!" "Good-bye friends!" Rhuna says. "I wish I could offer you more than thanks!" The landing party beams back aboard the ship.
When the Enterprise fires the Mind Module into the star, it explodes violently. Again, the ship is thrown into a void, where time and space intermingle. Then, they arrive back in their own universe! "We succeeded Captain!" Spock says, "We have once more crossed the barriers of superspace!" The Enterprise continues her mission, setting course for Draconis. "Rhona was quite a woman" the Captain thinks to himself. "If only infinity didn't block our paths..."