A plot by the rulers of the hopelessly overcrowded planet Gideon, who lured Captain Kirk aboard a replica of the Enterprise so that a disease in his blood could restore death to their world.
In the Original Series episode The Mark of Gideon, Kirk beams down to open membership talks with Gideon and instead finds himself on an apparently deserted Enterprise. The only other person aboard is a young woman, Odona. Meanwhile Gideon's ambassador Hodin insists to Spock that Kirk never arrived, and Starfleet and Federation officials refuse to let Spock search.
The empty ship is a full-scale copy built on the surface. The people of Gideon are almost immune to illness and regard life as sacred, so their population has grown until there is no room to be alone. Kirk once had Vegan choriomeningitis, and Hodin's council wants the virus to give their volunteers a means of dying.
Odona, Hodin's daughter, is infected and falls ill. Spock disobeys orders and beams down to find Kirk; McCoy cures Odona, who returns home as a carrier to do what Kirk was meant to.