When his colleagues, Charles Winlett and Derek Moberley, brought in a Krynoid pod, John somehow sensed that it was still alive and placed it under an ultraviolet lamp to thaw it out. This revived the pod and it infected Winlett, who slowly became a Krynoid himself.
John assisted the Fourth Doctor's investigations, but was forced by Scorby to hand over the second pod. When he tried to contact South Bend for help, the Krynoid that had been Winlett attacked and killed him. (TV: The Seeds of Doom)