The TARDIS narrowly avoids becoming engulfed in a cobwebby substance in space. It arrives in the London Underground railway system, the tunnels of which are being overrun by the web and by the Great Intelligence's robot Yeti. The time travellers learn this crisis was precipitated when Professor Travers, whom they first met in the Himalayas some thirty years earlier, accidentally caused one of the Yeti to be reactivated, opening the way for the Intelligence to invade again.

Public Eye is a British television series that ran from 1965 to 1975. It was produced by ABC Television for three series, and Thames Television for a further four series. The series depicted the investigations and cases handled by the unglamorous enquiry agent Frank Marker, an unmarried loner who is in his early forties when the series begins. In the words of an ABC trailer for the third series: "Marker isn't a glamorous detective and he doesn't get glamorous cases—he doesn't even get glamorous girls. What he does get is people who are in trouble—the sort of trouble you can't go to the police about, even if you are innocent."