Executive Producer: Gene Roddenberry
Producers: Gene L. Coon + John Meredyth Lucas
Associate Producer: Robert H. Justman
Script Consultant: D. C. Fontana

Writer: Robert Sabaroff
Dir.: Joseph Pevney

Captain Kirk: William Shatner
Science Officer, First Officer, Cmdr. Spock: Leonard Nimoy
Dr. Leonard "Bones" Mc Coy: DeForest Kelly
Lt. Sulu: George Takei
Lieutenant Commander Montgomery Scott: James Doohan
Lieutenant Uhura: Nichelle Nichols
Nurse Christine Chapel: Majel Barrett

Lt. Kyle: John Winston

Stardate: 4307.1

On their way to solar system Gamma 7 A the Enterprise is to find the reason why contact to the system is lost, Spock suddenly senses the death of 400 Vulcans on board of the Intrepid and says: "In the Gamma 7 A area, billions of people – all dead." The facts are not confirmed by the computer yet and Spock is asked how this can be possible when he did not have any physical contact. "I know that no person, no computer knows what had happened to them ... You find it easier to understand the death of one than the death of thousands. You speak of the hardness of the Vulcan heart, how little room is in yours? ... it might have rendered your history a little less bloody." 

Soon they approach a gigantic area which provides no data. The launched probe does not transmit any data as well. Kirk keeps on asking for facts – without results. In addition to the situation more and more people feel distressed and weaken. The ship looses power. Again Kirk's questions cannot help supplying dada and he says: "O. k., tell me what it is not." "It is no liquid, not material and not transparent." In front of them a zone of darkness. "Kindly tell me what happened to the stars!" It becomes obvious that this thing is responsible for the disappearance of the whole Gamma 7A area and the Intrepid. All crew - members are overtired and Scotty's announcement "We have lost 5 % of our energy" does not raise the mood either. So it seems to happen to the crew more and more. 

All lose energy and McCoy informs them that 2/3 of the people on board are affected to a greater extend. The Enterprise is drawn closer soon close enough to cross the boundary layer, Spock says. "The boundary of what?" he is asked. "Between where we were and where we are now." "Are you trying to be funny, Mr. Spock?" "It would never occur to me, Captain." Some worry how to stay alive and Kirk responds: "Our mission is not to stay alive but to investigate." McCoy adds: "According to the energy - meters we're all dying." Because any attempt to go backwards is a leap forwards Spock suggest to go forward full speed. Full power forward indeed makes the Enterprise slow down. The speed the ship is drawn towards the center is decreasing and Scotty supports the idea: "Anything is acting backwards." 

As Kirk and Spock talk about defeat, Spock says that Vulcan was never conquered. Vulcans do not know of such a past. Now Kirk asks him: "What did you sense when you knew they were killed?" " ... Astonishment." Scotty interrupts with the announcement that they still have got energy for 2 hours. Spock has got another message: "I cannot say what it is but I would say: 'It has found us'." Having crossed the boundary they look at something which seems to have a center: The size of the "thing" is 11,000 miles in length and 2–3 miles in width. 

Now Spock reads data: "Interior: Protoplasm; condition: Living." McCoy is awed: "It's an amoeba! It can reproduce ..." Spock: "This unknown lifeform is invading our galaxy like a virus." Kirk: "The Enterprise would lose power too quickly if we came closer..." McCoy: "We can risk a shuttlecraft..." A discussion begins about who is to go. Kirk: "I am better qualified because of commanding." "That makes you indispensable," Spock uses his argument. McCoy wants to use the chance to "research on the biggest laboratory in the universe" and Spock (who rather risks his life than watches one of his friends go ... as the others, none gives the true reason) tries to convince that he's best qualified. 

Captain Kirk takes a moment to consider whom of his two friends he is going to send out in a shuttle. He concludes that Spock is suited better, both physically and emotionally. He commands to prepare the shuttle and faces his two friends: "I am sorry, Mr. Spock." Gladly McCoy is ready to fetch all he needs as Kirk goes on: "I am sorry, Mr. Spock, that it is you who's going." Spock nods in agreement and leaves to get prepared. It is hard for McCoy to see Spock leaving alone for a mission he might not survive. But he cannot say so. 

Wish me luck, doctor

Though Spock experiences tremendous draining of his power, the failing of the shuttle functions and loss of its power, he manages to find the weakest spot of the center. Thinking that he will die, he shares his appreciation of the Enterprise and her officers and tells them that it was a pleasure to work with them. Knowing the weakest spot they fire antimatter into the center and kill the giant entity, killing it. Nearly dead, Spock makes it back to the ship, the life supporting system of the shuttle nearly expired. They all know a human would not have survived the mission. A discussion about a universe inside a universe ... begins.