Day 285: The Mind of Evil Episode 3

The villain in this story is The Master, making a return appearance. A running theme across much of our time with the Master is the issue of him recurring, an event which occurs regularly across the show.  But for now, it makes sense. The Master has been introduced as a force for evil on the Earth, and by having him be free at the end of Terror of the Autons, this could leave an uncomfortable hole in the fact that there is a force for evil loose on the Earth and the Doctor is doing nothing to stop this. By having the Master be the villain here, it reminds the audience of the fact that this person is serious and that he will be a constant pain in the Doctor's side. But I'll reserve judgment on whether his continued appearance is a good thing until after he's come back a few more times.