The Doctor Who episode “The Web of Fear” marked the return of the Yeti and the Great Intelligence, and the introduction of a character who would become a regular feature of the show in years to come: then Colonel Lethbridge-Stewart. The episode, in fact, has been considered the prototype for the main type of episode during the Pertwee era, when the Doctor would be confined to Earth for the most part.
The Great Intelligence and the Yeti were introduced in the episode “The Abominable Snowmen” which also featured a religious setting (a Buddhist monastery in Tibet). Here the Great Intelligence – essentially what in religious terms would be considered a bodiless spirit, or perhaps a demon – detects Professor Travers tinkering with the Yeti control sphere he had brought back with him from Tibet many years before, and this allows the Intelligence to home in on it and begin trying to make an entry into the world of humans once again.
The encountering of a character previously met, now older, is a great element to incorporate in a time travel story, and so it is great to see this done so effectively.
The Doctor, by the end of the episode, is disheartened that the Great Intelligence has only been cut off from Earth once again, and not defeated permanently as he had hoped. The Doctor’s plan envisaged the Doctor’s apparent sacrifice of himself to become the vessel for the Great Intelligence, when in fact he had reversed the wires in a helmet to be used for the procedure and thus hoped to defeat the Intelligence rather than be defeated by it. The idea of conquest through apparent self sacrifice which in fact lures the enemy to his defeat mirrors one classic interpretation of the significance of Jesus’ death.