Actor Frazer Hines contracted the chickenpox around the time this serial was being filmed and had to skip an episode. Normally this means the character just doesn’t appear, but the story needed Jamie for part two, so the producers cast a different guy in the role for this one show and were rather clever explaining why Jamie looked like a completely different man.
The thing is, a mysterious fellow known as “the Master” who is probably not the guy longtime Doctor Who fans think of as the Master, is manipulating the reality around our heroes after separating them. For Jamie, that means he sees a redcoat, his sworn enemy, but when he attacks, he is somehow turned into a cardboard cutout. Zoe finds a door and falls through into a pit on the other side. And the Doctor, well, the mystery man can’t seem to find him among the many weird trees all over the place.
That means the Doctor dodges some weird soldiers that look like giant toys, meets a hostile fellow who may be a certain Gulliver about his own travels, and eventually finds Jamie. But then he gets distracted because the whole world is speaking to him in pictographs and when he looks back, Jamie’s face is missing, so the Doctor tries to fix it with parts he finds nearby. And that would be why we get a different Jamie. See, that is clever.
Zoe’s door is found, but when a door is not a door it is a jar, transforming Zoe’s trap into a giant jar the two men can easily unscrew to help her out. Sure, she doesn’t recognize Jamie, but I don’t think Jamie recognizes Jamie at this point.
And the weird trees turn out to be giant letters spelling out cliches. Wherever they are, this place sucks.
But then they run into Gulliver again, and he’s clearly working for the Master, such that he seems to betray them when the soldiers come back. The Doctor, Zoe, and Jamie are then hustled off to a dark void where they see a unicorn, and it starts charging right at them. The Doctor tells the other two to stick together, but that horn looks awfully sharp…