John Stephenson was a botanist employed by the World Ecology Bureau. He and his colleagues Charles Winlett and Derek Moberly were working at an antarctic research station when the other two found a strange pod in the ice. After informing Sir Colin Thackeray and Richard Dunbar in London, they brought the pod to Stephenson, who, sensing life within, decided to attempt to cultivate it. The others cautioned against this, since Sir Colin was sending a specialist from UNIT, the Doctor, but Stephenson was insistent that the pod was their discovery and he didn't want UNIT involved.
Unfortunately, not long before the Doctor arrived with his companion Sarah Jane Smith, a weed which grew from the pod stung and infected Winlett, beginning to transform him into a Krynoid. Leaving Moberly to tend to him, Stephenson, the Doctor and Sarah went out to where Winlett and Moberly had found the pod, discovering a second one, which they chose to keep frozen.
Meanwhile, the slowly mutating Winlett killed Moberly and escaped into the antarctic wastes. Stephenson and the Doctor hunted him but failed to recapture him and he remained at large. Things took a turn for the worse when Harrison Chase's henchman Scorby and botanist Arnold Keeler arrived looking for the pod. Scorby found the empty, first one, but Stephenson accidentally let it slip that there was a second one. Scorby took everyone prisoner and demanded the second pod. They confessed when he threatened to shoot Sarah, and Scorby forced Stephenson to show him where it was.
After obtaining his prize, Scorby and Keeler took Sarah as a hostage and departed, leaving the Doctor and Stephenson tied up together. They managed to free themselves, and, while the Doctor went to rescue Sarah, Stephenson tried to call for help on the camp radio, not realizing Scorby had sabotaged it. As he attempted to get it functioning, Winlett, now fully mutated into a Krynoid, returned to the base and attacked him, strangling him to death.