Star Trek The Original Series S3 Ep 24 - Body Swaps

Season 3 Episode 24 Turnabout Intruder
When Kirk examines an apparatus in the room, Lester activates it. It traps Kirk into position on one side of it. Lester then rises from her bed and stands alongside Kirk on the apparatus and effects a life-entity transfer, each from one body into the other. 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. Lester/Kirk starts to strangle Kirk/Lester but is interrupted as the others return. Lester/Kirk disables the cell's force field and orders Kirk/Lester to come out as he/she will be the first to be executed, lying that the prisoners would be moved to different cells — supposedly to prevent further conspiracy. But before Lester/Kirk can kill Kirk/Lester with the hypospray, the life-entity transference wears off completely and Kirk, now in his own body, successfully prevents the murder. Lester, in her original body, collapses into enraged hysterics over her total, and now permanent, defeat.