They took nine hours to find the flaw, because there had to be one, and there was.
It was McCoy who said it. "It doesn't help us."
"Doctor..."
"No, listen, because I've been sitting here nine hours letting you two get excited, and somebody has to say it out loud. The old universe is down there under the floorboards. Fine. You can open the door and look at it. But Jim isn't in the old universe, Spock. Jim is in this one. He's in 1948, in the timeline that actually happened, the one we're standing in, and going down into the layer underneath does not get you within four hundred years of him."
"That is correct," said Spock.
"Then what in God's name are we celebrating?"
"We are not celebrating, Doctor. We are locating the lever."
Spock went to the board.
"You are entirely correct. Captain Kirk cannot be retrieved from 1948. He cannot be retrieved from 1930. The Guardian will not open those hours. They have been lived, and to unmake them would be a correction, and it will not perform one. But that is not the only door.
"In the timeline that was overwritten, there is a bridge. Aboard this vessel. Six hours before Doctor McCoy administers cordrazine to himself."
McCoy went very white.
"That bridge is a lived hour. It is fully present in the record. And it is not being corrected, because it has already been unmade. It is a dead layer. And the Guardian will open a dead layer, because opening a dead layer is not an alteration. It is a reading."
Nobody moved.
"And if somebody is standing on that bridge," McCoy said, and his voice had gone.
"Then the console does not overload," said Spock. "And you do not go over. And the hypospray is not in your hand. And the drug is not administered. And you do not run for the transporter room. And you do not go through that portal. And there is no man in 1930. And there is no Edith Keeler. And there never was."
"And the whole thing never happens," said McCoy.
"The whole thing never happens."
The silence in that laboratory went on a long time.
And then Montgomery Scott, who had not spoken in nine hours, said, quietly, from the back of the room:
"Aye. And what happens to Captain Pike?"