When scientists unearth two seed pods deep in the arctic permafrost, the Doctor and Sarah Jane rush to investigate. Soon the Doctor's worst fears are confirmed: the pods house Krynoids, one of the most parasitic and dangerous life forms in the universe. One of the creatures has already infected a scientist and now a hideous monster is rampaging through the Base, intent on total destruction.
When the second pod is stolen amidst the escalating carnage, it is transported into the hands of insane botanist Harrison Chase. From his mansion in England, the plant-obsessed Chase will allow the pod to split open. Both the ruthless millionaire and the rapidly growing carnivorous Krynoid are intent on infecting and destroying our entire world.