On the other hand, I could be wrong about that.
While many stories feature the Doctor visiting a planet or people he has prior, off-screen knowledge of, far rarer are stories focusing on the Doctor returning to witness the aftermath of his interventions. The First Doctor story “The Ark” shows the direct cause-and-effect of his presence by taking the Doctor into the future of a setting he has just visited (and disrupted); while the Third Doctor visits Peladon over the course of two disconnected stories, the latter relying heavily for its plot twist on the events of the former. But Chris Boucher’s debut script, “The Face of Evil” (Story Production Code 4Q), posits an entire adventure for the Fourth Doctor that viewers have not seen, the outcome of which drives the events of the story on offer.
The strength of “The Face of Evil”—and indeed, it is the strongest story of Tom Baker’s reign to date—comes from the careful parcelling out of this “hidden” story about the mistake the Doctor made at some point in the past, a catastrophic error that resulted in generations of strife between the Tribe of Tesh and the Tribe of the Sevateem on this nameless planet. More interestingly, the Doctor himself doesn’t realize his past role in the proceedings until partway through the story, such that the sudden appearance of his face carved into a cliffside comes as a shock to him as well as to the viewer. This cliffhanger, shrouded as it is in genuine mystery, creates more tension than any end-of-episode monster revelation ever could.
Though Boucher slowly unveils the Doctor’s past mistake while simultaneously establishing two different factions in the Tesh and the Sevateem, he and director Pennant Roberts keep the story, rife as it is with exposition, moving quickly, a task aided by Louise Jameson’s introduction as Leela, the new companion. The first non-contemporary companion since Jamie and Zoe were returned to their worlds at the end of “The War Games,” Leela brings a much-needed spark to the series, representing as she does a different moral and ethical system. Very little conceptual daylight exists between the Third and Fourth Doctors and Liz, Jo, and Sarah Jane; they, and the audience, broadly see the world the same way as the Doctor(s), and any arguments between them hinge on philosophical nuances. By contrast, the Doctor here has to warn Leela to stop killing people as a matter of course.
As with the Second Doctor and Jamie, Leela’s non-technical background as a member of a hunter/gatherer tribe allows for more seamless exposition, giving the Doctor (and writers) a reason to avoid too much technobabble. But where Jamie at times seemed bored with the futuristically fantastical and eager to get on with the action, Leela comes across as curious, open-minded, and fearless; the story opens with her rejecting the orthodoxy of the Tribe of the Sevateem, denying the divinity of Xoanon and being banished as a result. Given the sartorial choices of the shaman who speaks for Xoanon, though, it’s not hard to understand her doubts…