The fourth serial is arguably the first of the Hartnell ‘pure historicals’; stories set in the then-past that contain no science fiction elements beyond the presence of the time travellers. This, of course, assumes that you don’t consider
100,000 BC separately from the first episode, although, if you want to be really nitpicky, “prehistory” also isn’t quite the same thing as “history”, either. At least as significantly, it’s the first “missing story”, with only the soundtrack surviving in its original form. Fortunately, that’s enough for us to be able to experience it in some limited way, and certainly sufficient for what I’m doing here.
Where & When
The story is set in 1289, earlier than most modern series historical settings, although not remarkably so. It involves an epic journey, taking the protagonists from the Pamir Mountains, through the Gobi Desert, and across China to eventually reach Beijing. It refers to China by the name that Marco Polo used for it historically and that was standard in Europe at the time – Cathay.