The Mind of Evil

STORYLINE

The Doctor and Jo are investigating a revolutionary new way of treating psychotic criminals at Stangmoor Prison - a machine invented by one Professor Keller that literally sucks the evil out of a man's brain. But when the process is complete, what is left behind - a saint or a simpleton?

It transpires that Professor Keller is the Doctor's arch-enemy, the Master. The machine actually houses a deadly mind parasite that the Master has taken to Earth for his own evil ends. He intends to use it to sabotage the global peace conference UNIT is policing, thus bringing Earth to the brink of war. And when he takes over the prison and hijacks a missile that could wipe out half of Europe, it seems the cards are stacked firmly in his favor.

Meanwhile, the mind parasite is growing stronger all the time, killing anyone in its path by making them experience that which they fear the most. Can the Doctor defeat both the Master and the parasite while preventing the world's major powers from embarking on all-out nuclear war?