For the 16th season of classic Doctor Who they decided to have an over reaching seasonal arc called the Key to Time. In it The Doctor and his companion Romana must collect six keys for a mysterious White Guardian in order to restore balance to the universe. They keys are hidden across time and space (of course).
I love the idea of a long arc like that, but unfortunately they incorporated it very poorly. Essentially the season tells its usual set of multi episode stories with The Doctor running about having adventures but with the various keys more or less tacked on as an after thought.
The final story, The Armageddon Factor spends a little more time sussing out the larger concept, but just barely and its got an ending that is so disappointing I’d be hard pressed to find a more miserable seasonal closer.
The Doctor and Romana land on a planet that is involved in a long and costly war with a nearby planet. They have a little fun with that story for a bit until they discover a third “evil” planet ruled by “the Shadow” who turns out to be an agent of the Black Guardian. More stuff happens. Most of it not that interesting.
They jury rig the last piece of the Key to Time in order to stop nuclear annihilation. That’s actually a lot of fun as the broken key can’t hold the weapons in place for too long so they sit in an increasingly larger time loop. But they waste so much of the story showing us the countdown clock over and over again it winds up being disappointing.
Its really not a great story and it caps off a fairly disappointing season. Still, I can never be too hard on these Classic Who episodes and there are some fun bits including a few scenes where K-9 has to pretend that The Shadow is his real master.