Turnabout Intruder ( episode ) A mad scientist tries to take control of " Enterprise " by switching bodies with Captain Kirk . ( " Series finale " ) Summary . Teaser . The " Enterprise " answers a distress call from an archaeological expedition on Camus II and a landing party beam s down . Captain Kirk finds that Janice Lester , whom he knows , is gravely ill , and Doctor Arthur Coleman is tending to her . Lester awakens just as Spock ' s tricorder picks up faint life - form readings . Lester becomes unquiet and Dr . McCoy suggests that Kirk stay with her while the others leave to investigate the readings . Kirk and Lester reminisce about their time together at Starfleet Academy , Lester still resenting her inability to rise to a captaincy . When Kirk examines an apparatus in the room , Lester activates it . It traps Kirk into position on one side of it . Lester takes a place alongside Kirk on the apparatus and effects a life - energy transfer , each from one body into the other . Act One . Lester ( in Kirk ' s body ) discloses to Kirk ( in Lester ' s body ) her plan to command the " Enterprise " , as well as her willingness to kill . She starts to strangle Kirk but is interrupted as the others return . McCoy reports that the rest of the staff on the planet are dead of exposure to celebium , though Coleman says that this is unclear , a disagreement that will affect the choice of treatment . The survivors beam back to the " Enterprise " . Lester , in Kirk ' s body , orders that a medical team stand by in the transporter room for Kirk in Lester ' s body . In sickbay , Lester and Dr . Coleman discuss Kirk , whom they want to keep from reawakening . Coleman knows Lester ' s plans , and in fact knows both that celebium was the lethal agent and that Lester had caused the deaths by sending the personnel to where the celebium shielding was weak . On the surface of Camus II , Coleman had kept the rest of the landing party apart to give Lester time enough to kill Kirk , but he refuses to induce Kirk ' s death . McCoy arrives and is surprised to see the captain in sickbay . Lester , in Kirk ' s body , transfers responsibility for the patient ' s care to Dr . Coleman , despite McCoy ' s strenuous protests . The patient regains consciousness , but Coleman orders Chapel to administer a sedative . Act Two . The impostor Kirk orders Sulu to execute a course change for a hospital on Benecia Colony , even though Spock points out that a course for Starbase 2 would provide a better radiation treatment without delaying the rendezvous with the " Potemkin " at Beta Aurigae . The new Kirk reacts sternly to being informed of the consequences of his orders . The captain next meets with McCoy in Kirk ' s quarters , who defends his qualifications to treat Lester and has discovered that Coleman was relieved of duty as a chief medical officer on a starship due to severe incompetence . The captain says his decisions stand but McCoy uses his authority to order the captain to a medical examination based on " " emotional instability and erratic mental attitudes since returning from that planet . " " The captain calls this revenge , but the confrontation is interrupted as he is recalled to the bridge . In sickbay , Kirk as Lester again regains consciousness and calls for McCoy . Dr . Coleman says he is in charge and tells Nurse Chapel that Kirk ' s claims are symptoms of a paranoia that has been developing for six months . He tells Kirk , " " You are insane , Dr . Lester . " " He orders the nurse to keep Dr . Lester under constant sedation . Act Three . Kirk , in Lester ' s body and working not to seem paranoid to Nurse Chapel , asks to meet with McCoy or Spock , but is alarmed to hear in passing of the course change ordered for the " Enterprise " . After Chapel leaves , Kirk escapes from his restraints by breaking a glass and using it to cut them . Nearby , McCoy discusses with Spock his plans to run tests on " Kirk " . News of the captain ' s aberrant behavior is spreading around the ship , and both of them are convinced that a rapid - onset mental illness began during Kirk ' s brief time alone with Lester on Camus II . The patient approaches the two – but the captain had arrived a moment earlier . Lester orders Kirk to be placed in isolation with a twenty - four - hour watch . Soon , however , Spock arrives at the cell to question the prisoner . Lieutenant Galloway concedes Spock ' s point that isolation orders have never applied to the " Enterprise " s senior staff . Kirk calmly explains to Spock the technology of life - entity transfer , " " accomplished and forgotten long ago on Camus II . " " When Spock protests that Starfleet requires objective evidence , Kirk describes events from their common past , such as their encounter with the Tholian s and also the Vian s , then finally , he invites the Vulcan mind meld . Performing , then breaking , the meld , Spock is convinced and asks Kirk to come with him . Galloway tries to block this . Spock disables him with a Vulcan neck pinch , but not before Galloway can call for help . The captain passes McCoy ' s physical , but McCoy insists on performing the Robbiani dermal - optic test to compare to a previous test . This , too , reveals nothing . Then they hear on the intercom that the prisoner has escaped . The captain goes to the cell , Spock surrenders , and the captain broadcasts throughout the ship a call for an immediate court martial of Spock on the charge of mutiny . Act Four . The court martial convenes in a briefing room . Scott interrogates Spock , who describes his telepathic evidence that Kirk and Lester have exchanged bodies . Scott tells Spock that Starfleet Command will need more concrete proof than that . Later , McCoy testifies that the captain ' s physical and mental state are as they were when he assumed command of the " Enterprise " . Spock ' s logic compels Lester to call Kirk out of isolation to testify . Kirk describes the life - entity transfer , but Lester interrogates him in such a way so as to ridicule him . Lester accuses Spock of inventing the life - entity transfer controversy to assume the captaincy . Spock asserts his intent to reveal the truth and oppose the captain . Lester regards this as an overt confession of mutiny , but as she makes this clear , she sounds increasingly irrational . She declares a recess , followed immediately by the vote . In the corridor , McCoy and Scott agree that the captain ' s state of mind is unprecedented , Scott admitting to never having seen the captain " " red - faced with hysteria . " " Scott asks McCoy what the captain will do on losing the vote , concluding that " " we ' ll have to take over the ship " " and conceding that that too will be mutiny . But Lester is recording the conversation and extends the mutiny charge , and orders the death penalty to them . Chekov and Sulu protest that the death penalty is expressly forbidden , except for General Order 4 , which has not been violated by any " Enterprise " crewmember . The enraged Lester angrily orders that the other senior officers return to their posts and has Spock , Scott , McCoy , and Kirk detained in a holding cell by Lemli to await execution . Lester schedules a group execution on the hangar deck , with interment to take place on Benecia , but Sulu and Chekov take their hands away from their helm and navigation console s in defiance . But just then , the life - entity transfer temporarily reverses , as Kirk senses it briefly in the holding cell . Lester runs to meet Dr . Coleman in the archaeology lab to tell him the transference is weakening . Coleman says the only solution is to kill Lester ' s body but again refuses to do so personally . However , Lester says Coleman is complicit in many murders and now has no choice . He gives Lester a phaser and prepares a doubly lethal hypospray and the two proceed to the detention cell . Lester disables the cell ' s force field and orders Kirk to come out , to be the first to be executed , lying that the prisoners would be moved to different cells , supposedly to prevent further conspiracy . But before she can kill Kirk with the hypospray , the life - entity transfer breaks and reverses for good , and Lester weeps over her defeat . Kirk lets Coleman accompany Lester back to sickbay to care for her and laments her sadness . Memorable quotes . " " Your world of starship captains doesn ' t admit women . " " " " I loved you . We could ' ve roamed among the stars . " " " " We ' d have killed each other . " " " " It might have been better . " " " " Believe me , it ' s better to be dead than to live alone in the body of a woman . " " " " Youth doesn ' t excuse everything , Doctor McCoy . " " " " Love ? Him ? ! ? I loved the life he led . The power of a starship commander . It ' s my life now ! " " " " You are closer to the captain than anyone in the universe . " " " " You are not Captain Kirk . You have ruthlessly appropriated his body , but the life entity within you is not that of Captain Kirk . You do not belong in command of the " Enterprise " , and I will do everything in my power against you . " " " " You have heard the statements you put into the record . Do you understand the nature of it ? " " " " I do , sir . And I stand by it . " " " " It is mutiny ! " " " " On the basis of these statements , I call for an immediate vote , by the powers granted to me as Captain of the " Enterprise " . A recess is declared , to be followed by a vote . " " " " Yes , sir . An immediate vote before our chief witness can be left to die on some obscure planet with the truth locked away inside of her . " " " " Silence ! You will be silent ! ! A recess has been declared . There will be no cross - discussion . When I return , we will vote on the charge of mutiny . The evidence presented here is the only basis of your decision . " " " " Doctor , I ' ve seen the captain feverish , sick , drunk , delirious , terrified , overjoyed , boiling mad . But up to now I have never seen him red - faced with hysteria . " " " " Headquarters has its problems , and we have ours . And right now , the captain of the " Enterprise " is our problem . " " " " We ' re talking about a mutiny , Scotty . " " " " Aye . Are you ready for the vote ? " " " " Yes , I ' m . . . I ' m ready for the vote . " " " " The death penalty is forbidden . There is only one exception . " " " " General Order 4 ! It has not been violated by any officer on the " Enterprise " ! " " " " The bridge is where you belong . " " " " Oh , I ' m never going to be the captain , never . . . kill him . . . " " " " You are . . . you are as I loved you . " " " " I didn ' t want to destroy her . " " " " I ' m sure we all understand that , Captain . " " " " Her life could have been as rich as any woman ' s . If only . . . if only . . . " " Links and references . References . archaeology ; arrest ; bad dream ; Benecia ; Benecia Colony ; Beta Aurigae ; binary system ; blood count ; blood pressure ; " Bones " ; Camus II ; Camus II staff ; celebium ; celebium shielding ; Coleman ' s former post ; color wavelengths ; conspiracy ; court martial ; death penalty ; delirium ; delusion ; demotion ; disorder ; distress call ; drunk ; emotional structure ; execution ; exercise table ; expedition ; fever ; General Order 4 ; gland s ; hangar deck ; hearing ; heart ; hysteria ; insanity ; " in the pink " ; kidney ; life - energy transfer ; liver ; logic ; malpractice ; metabolic rate ; meter ; Milky Way Galaxy ; Minara ; murder ; mutiny ; nail file ; NGC 602 ; paranoia ; ; promotion ; pulse ; radiation poisoning ; recess ; Robbiani dermal - optic test ; sedative ; smothering ; specialist ; Starbase 2 ; Starfleet Command ; Starfleet Headquarters ; Starfleet Regulations ; Starfleet Surgeon General ; surgeon ; Tholian sector ; Vian s ; Vulcan mind meld ; Vulcan neck pinch Unreferenced material . trump card