He and Jan were drafted to fight the Daleks, but were offered drugs that were supposed to give psychic powers to avoid fighting. Christopher took his share and gained immense psychic powers, but lost his sex, becoming neither male nor female. He was killed by the Hoothi while in Puterspace but became one with Puterspace and could use his psychic abilities to control his corpse for a short time while remaining undetected.
While the Seventh Doctor and Ace were trapped in Puterspace, the Doctor asked a projection of Julian Milton to imagine the form of Christopher. Christopher's mind took on this body and helped the Doctor and Ace escape. When the Doctor entered Puterspace again, he used Brother Phaedrus to summon the Hoothi sphere into Puterspace and to make contact with Jan Rydd. Jan then blew up the sphere, saving the universe. He died shortly afterwards. (PROSE: Love and War, AUDIO: Love and War)