The Saturnian plague broke out on Titan Base in 4920. Hector, possessed by the Swarm, brought the TARDIS there. Ace caught the plague, so the Seventh Doctor took them to the Bi-Al Foundation. This ensured the Swarm's creation, as it had mutated from the plague. (AUDIO: Revenge of the Swarm)

Community content is available under CC-BY-SA unless otherwise noted.