Count Scarlioni reveals his true form as Scaroth, the last of the Jagaroth and uses his time machine to go back in time and rewrite history. The Doctor, Romana and Duggan take to the Tardis in a race against time to stop him.
Scaroth, the last of the Jagaroth, forces Romana to build a field interface stabilizer for his time machine. Romana reluctantly does so, not knowing that the full extent her action will lead to the total non-existence of all life on Earth. Humans will never have existed.—statmanjeff