Still looking for a way out of E-Space, the TARDIS crashes to Isenfel - a realm of snow and ice. Snarling beasts stalk the frozen plains, a feisty princess leads the hunt, and a queen in an ice palace rules over her loyal subjects.
But this is no fairytale kingdom, and everyone in Isenfel knows the price of survival. While Nyssa and Tegan uncover deadly secrets hidden in the palace, Turlough flees for his life across the tundra.
And as for the Doctor... he only ever wants to change things for the better. But in a world such as Isenfel, such a hope may not even be possible.
Equilibrium contains examples of:
- Action Girl: Princess Inger is one of her kingdom's primary hunters, being particularly deadly with a bow and arrow.
- Appease the Volcano God: A variation, with the people of Isenfel regularly sacrificing their own people to maintain "The Balance", as any long-lasting increase in population results in deadly snowfall that vaporizes anything it touches.
- Aw, Look! They Really Do Love Each Other: Tegan may happily complain about Turlough and argue with him until she's blue in the face, but she doesn't hesitate to ride out into the snowstorm and risk facing the deadly snowbeasts so she can find and rescue him.
- Blue Blood: Queen Carlina, naturally. She recognizes after only a few conversations that Nyssa comes from noble upbringing as well.
- Call-Back:
- Tegan doesn't need help getting onto or riding a horse, having had quite a lot of practice recently.
- Nyssa and the Doctor bring up Adric's death.
- Call-Forward: Turlough's intense dislike of snow and the cold will be explored further in "Singularity".
- Cliffhanger: Tegan has been kidnapped by mysterious, silent figures who descended on Isenfel in a spaceship.
- Dropped a Bridge on Him: Solis, whom the Doctor was tracking at the end of "Mistfall", made it to Isenfel and was killed shortly after arriving to maintain the balance.
- Girl of the Week: Inger for Turlough.
- Heroic Sacrifice: Romy throws herself into the black snow, giving up her life to stop the advance of destructive energy and give everyone else a chance to escape.
- Human Sacrifice: Such an accepted part of Isenfel society that those chosen for "balancing" don't even try to argue, merely accepting their fates quietly.
- Immediate Sequel: Picks up right where "Mistfall" left off, with the TARDIS going down in a crash landing.
- Just Before the End: The universe of E-Space is dying, slowly but surely being consumed by entropy energy. The Kingdom of Isenfel is one giant experiment in trying to hold the destructive power off.
- No Antagonist: Very rarely for a Doctor Who story. The closest things to bad guys are the Black Snow Beasts, and they're just mindless animals and glorified computer subroutines.
- Really 700 Years Old: Skaarsgard isn't just Isengard's Balancer, he has always been Isengard's Balancer.
- Royals Who Actually Do Something: Princess Inger takes care of her people by going out and hunting their food herself, and is a highly accomplished warrior of the kingdom.
- Single-Biome Planet: Isenfel is described as a living snowglobe, with ice and snow covering everything in sight.
- Shout-Out:
- Tegan remarks that the exclusively white, fair-haired denizens of Isenfel look like an ABBA tribute night.
- Tomato in the Mirror: Balancer Skaarsgard discovers that his unnaturally long life is because he isn't human at all, but is a highly sophisticated android.
- Trailers Always Spoil: The end result of Tegan's cliffhanger kidnapping was a Foregone Conclusion anyway, but the trailer for the next episode makes it clear that she will be reunited with the TARDIS team.
