The Doctor, Romana and K-9 arrive on the forest planet Tygella, where the native Tygellans now live in a underground city, due to the carnivorous plants. Where the Doctor finds he has been wrongly accused of stealing the Dodechedron, the city's power source. Only to discover the culprit is Meglos, the cactus-like last survivor of the desert planet Zolfa-Thura and he...