Equilibrium was the one hundred and ninety-sixth story in Big Finish's monthly range. It was written by Matt Fitton and featured Peter Davison as the Fifth Doctor, Sarah Sutton as Nyssa, Janet Fielding as Tegan Jovanka and Mark Strickson as Turlough.
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.
The TARDIS is going out of control as the Doctor, Tegan, Nyssa and Turlough pursue Pik Solus who has stolen the TARDIS's interface stabiliser and track him down to Isenfel where they are forced to land and go off in search of help when the TARDIS falls through the ice and becomes irretrievable. They are found and rescued by Inger who takes them back to her mother's castle. Nyssa mentions to the Doctor that she dropped the interface stabiliser while they were being chased by some wolf-like creatures earlier. They are then introduced to Queen Karlina (Inger's mother) who is interested in the Doctor claiming to be a man of 'learning'. The Doctor seems more interested in the fact that they are not the first arrivals as the queen mentioned that someone else had arrived just some time before. Karlina in the meantime consults Balancer Skaarsgard who informs her that the equilibrium has been upset and is awaiting readings from his machines.
Balancer Skaarsgar then consults Jesper, who had seen the visitors, for his opinion. Turlough wanders the castle and is found by Inger who attempts to court him by inviting him to a night hunt, which he politely declines.
Inger teases him that he will succumb eventually. Tegan and Nyssa are lead to their quarters when Tegan claims she hears something roaming the caslte but is assured not to worry. They are prompty summoned to the feast being held in their honour. The Doctor and Karlina converse when they are joined by the pair and the Doctor inquires more about the proceedings of Isenfel and the stranger that was found, whom he correctly guesses to be Solus and discovers that Solus did not survive the crash. The Doctor asks about the interface stabilizers but recieves no confirmation of its finding.
The Balancer arrives and Karlina explains that it is time for maintaining equilibrium, and since four strangers have arrived, they must execute four of their own, but the Doctor tries to intervene...
The Doctor interrupts the process saying they cannot murder for the sake of "balance" and the Queen postpones the execution for a while yet while the Doctor tries to find another way. Tegan is distraught about how the servants were willing to discard their life for the sake of balance and while Nyssa tries to explain to her that it may be their tradition and it's not their place to change it, they go off to find out what is going on at Tegan's behest. The Doctor gets a reluctant Turlough to go hunting with Inger to keep her distracted while he figures out a way to change their fundamental societal belief. Karlina consults Balancer Skaarsgar who is worried that the machine now reads "re-calibrating" which he has never seen before. She reminisces over her deceased husband and Balancer Skaarsgard accuses her of clinging tightly to the stranger in hopes he may explain what the machine does and the underlying science, something that greatly disturbs and upsets the Balancer. Turlough spots black snow which Inger explains is Isenfel's way of restoring balance if they themselves do not, claiming it is the peasants own fault to a disturbed Turlough.
Karlina takes the Doctor to the balancing room and explains to him that Isenfel always has the same number of people, animals, crops, etc and they keep meticulous count or else the planet does the job for them. The Doctor then finds out that Solus was put to death because Karlina found no reason to sacrifice a healthy subject for the sake of a sick and injured one. The Doctor is utterly disgusted and begins messing with the machine much to the Balancer Skaarsgar's chagrin, while Turlough and Inger encounter strange black beasts of colour similar to the snow they saw earlier, however, Inger does not recognise them and they attempt to flee. The Doctor inquires who was the Balancer before Skaarsgar but discovers it has always been Skaarsgard and manages to return him to his true form and takes his key, finding out that the machine controlling equilibrium is far more advanced than he thought. Tegan and Nyssa discover children in the castle and discover that Jesper and Romy have been hiding them because they believe the royals have always been shielded from the balancing so they hide them in the castle so that the families do not have to suffer by being executed to make room for the children. However, they are trapped and about to be killed by Jesper. Turlough and Inger are trapped by the beasts and while Inger embraces death as a royal, Turlough panics as there is nowhere else to go...
The Doctor and Karlina arrive in time to stop Jesper but the queen is taken aback at discovering the children, while the Doctor explains he has re-calibrated the machine to compensate for a new energy level (apparently it killed off life-forms in order to maintain a constant balance of energy on Isenfel) and they found them using the machine's map of all life-forms on the planet. The creatures pursuing Turlough and Jesper are suddenly absorbed back into the energy field and the two hurry back to the castle to explain what they saw. Tegan and Nyssa feed the children and Romy explains to them the way Isenfel works. Nyssa is asked to join the Doctor, leaving Tegan to talk with Romy some more. Skaarsgard is brought back online by the Doctor but bemoans the people he condemned to death, however, the Doctor assures him that it wasn't his fault and that if he hadn't done what eh did, everyone would have died. Nyssa arrives and the Doctor explains that Isenfel he suspects is an experiment that had been abandaoned and the inhabitants like lab rats. He instructs Nyssa to work on the re-calibration while he goes to comfort Skaarsgard and when Nyssa reminds him about the TARDIS he says he has a shrewd suspicion that it was what is causing the disturbance due to its power and that he hasn't forgotten. The Doctor finds Karlina and asks for Skaarsgard who has gone to rest. The Doctor then asks Karlina to take a team to recover his TARDIS from under the ice which she obliges but Skaarsgard arrives and offers to help the Doctor find the object he is seeking as the Doctor asked earlier, but only when the Doctor has explained to him what he is. Nyssa and Karlina go to find the TARDIS while Turlough and Inger discover the energy barrier and attempt to get back to the palace while Jesper, Tegan and Romy spot a large storm brewing and Romy believes it is her fault for taking the children away from the castle and sacrifices herself to the brewing storm thinking it will stop the blizzard from moving. Miraculously it does stop is and Tegan stops Jesper from following and gets him back on track to save the children.
The Doctor probes Skaarsgard's systems and discovers he was modeled after the original experimenter who was performing the experiment to understand the entropy decay of their universe as they discovered that it was occurring at a rapid rate and they were looking for a way to stop or slow it. Nyssa arrives and finds the Doctor in a panic as he explains that Isenfeld was an experiment meant to put off the entropic collapse, however, by raising the energy threshold he has triggered the inevitable and caused Isenfeld to collapse having now registered in its system as a failure. He panics as he has essentially condemned the people of Isenfel to death...
Turlough and Inger continue to attempt to get back to the castle while the Doctor and Nyssa try to figure out what to do next. Tegan and Jesper attempt to find Turlough with no success but Tegan has faith he's found a way to survive but they are chased by the black creatures. Tegan and Turlough find Nyssa and Karlina who have saved the TARDIS and they try to figure out where to go as the TARDIS isn't functioning. The Doctor laments about his inability to rescue them, seemingly having condemned them but Nyssa assures him that he is good and only wanted to help as that is what he does best, having helped her and many others and says he'll figure out something. Tegan and Jesper suddenly spot a ship coming through the barrier. The Doctor reconvenes with Nyssa and Turlough, Inger and Karlina and explains he has rigged up a device that can temporarily stabilise the dimensions of the TARDIS enough-so that he can transport everyone away from Isenfel. However, Karlina is reluctant to leave and demands time to think it through. Nyssa encounters Skaarsgard again and while he is unsure about his future, Nyssa assures him that he can still learn and adapt and that he should be with his people. Karlina and Skaarsgard share an intimate moment and he convinces her to leave for the sake of her people and herself. They depart on sad but friendly terms.
Tegan and Jesper attempt to enter the spaceship but Tegan is abducted. Karlina arrives and gives her approval for her people to depart but says she will be staying and that Inger is in charge, however, the black creatures surround them and the TARDIS while the Doctor is inside installing the temporary stabiliser. The creatures realise that the TARDIS is the largest source of energy and attempt to breach it while its dimensions are weakened and the Doctor attempts to hold them out. Karlina, taking control of the machine, draws the creatures away while they realise that it is Skaarsgard who has given his own life to keep Isenfel aloft.
Isenfel is saved and the Doctor instructs Nyssa to make sure the balancing machine is off for good and tells Turlough to say his goodbyes. Karlina, meanwhile, prepares to be killed by the creatures but they suddenly vanish. Convinced her time is over, she continues towards the mountain's edge regardless.
Turlough says his goodbyes to Inger who reciprocates with a passionate kiss when they are interrupted by Jesper who explains that Tegan has been abducted by the spaceship they saw earlier. The Doctor and Nyssa, meanwhile, discuss moving the people of Isenfel but come to the conclusion they'd rather stay on Isenfel. They suddenly realise that amidst the chaos they'd lost track of Tegan, when Turlough arrives to inform them of the bad news.
Tegan, trapped aboard the spaceship cries out for help....
- The Doctor - Peter Davison
- Tegan - Janet Fielding
- Nyssa - Sarah Sutton
- Turlough - Mark Strickson
- Karlina - Annette Badland
- Balancer Skaarsgard/Viktor Skaarsgard - Nickolas Grace
- Inger - Joanna Kirkland
- Jesper - John Albasiny
- Romy - Ella Kenion
- Tegan sarcastically refers to the people of Isenfel as looking like they were having an ABBA tribute night due to their blond hair and blue eyes.
- Turlough does not know how to ride a bicycle.
- Borusa always said that the Doctor's ability to understand logical systems far surpassed his ability to explain them.
- Nyssa uses the TARDIS scanners to find lifeforms.
- Turlough compares Isenfel to a petri dish.
- Turlough receives a passionate goodbye kiss from Inger.
- This story was recorded on 26 & 27 June 2014 at The Moat Studios.
- The cover illustration for this audio story was designed by artist Will Brooks.
- This story was originally released on CD and download.
- Tegan refers to the fact that Pik Solus stole the interface stabiliser on Alzarius. (AUDIO: Mistfall)
- After Pik Solus crashed his planet hopper on Isenfel, Balancer Skaarsgard killed him to maintain equilibrium. (AUDIO: Mistfall)
- Nyssa refers to Adric's death. (TV: Earthshock)
- Nyssa mentions she is "a lot older than she looks", and Queen Karlina claims she has "old eyes" like the Doctor. Nyssa looks younger thanks to being rejuvenated in India in the 1920s. (AUDIO: The Emerald Tiger)