Can we pause a moment and consider what we are watching here? A half alien's brain was removed by a chick in metallic purple thigh-high boots, the brain's owner walks around whenever a universal remote is waved in his direction, and now they're going to put the brain back? Good night!
Deep Purple complains that she can only take things out, she can't put them back in. It's like an aptitude test with blocks and stuff. Bones confirms that her brain -- like the brains of the rest of the FM Boots Brigade -- are atrophied from lack of use. It turns out that Deep Purple "put upon [her] head the Teacher" in order to perform the surgery. The Teacher is this big half-globe made out of Plexiglas. It has metal spikes sticking out of it. It looks like something Walter Mitty made in his garage. Spock's brain tells them that the Teacher contains recordings of the all the knowledge of the builders of this place. Not without much freaking and squawking on behalf of Deep Purple, Kirk forces the Teacher on Deep Purple's head. Reaction shots all around. Deep Purple opens her eyes. That must've taken considerable effort, given how heavy her eye shadow is. The Teacher removes itself from Deep Purple's head and she speaks clearly, concisely, and with articles about how the Teacher uses Spock's brain and so on and so forth. She then points a phaser at him. Scotty notes that it's set to kill. "So it is, that is the knowledge YOU have brought me," Deep Purple comments. Oh, the folly of the violent man, how it follies around. Kirk and Deep Purple argue about whether she should kill them and what will happen to Spock. Deep Purple says, "I do not know killing, I do not wish to kill." Suddenly, Scotty becomes a southern woman in a corset and swoons. Deep Purple is distracted by his "uggggh" and Kirk grabs the phaser back. Ah, but Scotty's swoon was a ruse! A ruse! Kirk orders Deep Purple to help them. "You MUST put BACK what YOU have TAKEN!" Deep Purple won't betray the FM Boot Brigade. In three hours her knowledge will leech away and she will be reduced to talking like a baby again. Bones thinks he can put the Teacher on and get the knowledge to put Spock's brain back. Spock's brain argues that it's risky, since Deep Purple is an alien and Bones is not. Bones insists, and even cites a greater good of bringing the knowledge of brain transplants to the world.
Bones puts the Teacher on. He stands for a moment while the music crescendos, and then he falls to his knees. Judging by the look on Kirk's face, he's experiencing sympathy pains. Bones pulls himself together and is all, "Scalpel!" Kirk is thrilled, and expresses this by gripping Bones' shoulder spasmodically.