Jon Pertwee's Doctor has always been a Doctor in control, more so, perhaps, than any of the other Doctors. So to see him being forced to march around in a circle at the bidding of the Great One, despite his vain attempts to resist her will, comes as a bit of a shock. Then, when the Great One points out the fear in The Doctor's mind, you know that, for the first time, the Third Doctor is in over his head.
It may have taken up until Pertwee's penultimate episode to put him in a peril that he couldn't get out of, but it was the only way to but the Third Doctor in a believable enough situation for him to not be able to get out of. As it's so rare to see Pertwee's Doctor have to face situations like these, I genuinely fear for him, too, because he is completely out of his comfort zone.
There's a magical scene in this episode when The Doctor meets his old mentor, the one he mentioned in his monologue in the last episode of The Time Monster. It doesn't hurt that the link between the two stories is enforced by the casting of George Cormack as K'anpo Rimpoche, as Cormack , ironically, playing King Delios, was cast into The Doctor's cell in The Time Monster, thus interrupting the monologue! The Doctor's admission to K'anpo of the fact that he stole the Metebelis crystal, not found it, is particularly notable. Just as the Second Doctor was being held accountable for his actions at the end of his era (in a literal sense), so, too, is the Third Doctor being held accountable for his. However, instead of a court of Time Lords being his judge, jury, and executioner, those roles are being played by his own actions. Only The Doctor could have set these events in motion, and only The Doctor can stop them now.