The Gideons are from the planet Gideon located in the Alpha Quadrant. They are extremely isolationists. They have very long life spans and don’t become ill. If they become injured, they heal quickly.
They had a severe over-population problem. They had decided to use the U.S.S. Enterprise captain, Captain James T. Kirk to introduce Vegan choriomeningitis into their population.
The prime minister, Hodin, used his own daughter, Odona, to introduce the disease. Hodin hope to use Kirk to introduce the virus into the general population of the planet. The ruling council took several months to devise this plan.
The crew of the Enterprise found out what happened to their captain. They rescued him. Captain Kirk ordered Doctor Leonard McCoy to cure Odona but left her as a carrier of the disease.