Among The Doctor’s enemies, Queen Xanxia would unquestionably be considered one of the most selfish and ruthless beings he ever thought, as she thought nothing of destroying entire planets simply to ensure that she herself would live forever (Even The Master at his worst only tried to destroy one planet to ensure his own survival (“The Deadly Assassin” and “The Keeper Of Traken”).
The queen of the planet Zanak, Xanxia was regarded as evil even during her own lifetime, committing unspecified atrocities in the name of her own survival. Having somehow extended her life by hundreds of years, Xanxia was nevertheless approaching death by the time she gained an unexpected bonus in the form of a ship crash-landing on her planet, discovering a survivor among the wreckage in the form of the ship’s Captain. Using her technological resources, Xanxia was able to rebuild and repair the Captain’s shattered body to transform him into a cybernetic form, the left side of his body now mostly artificial, extending his life-span while allowing her control of him thanks to her ability to deactivate or influence his mechanical components if he should try and rebel against her.
The most significant detail about her new subject, however, was the fact that the Captain’s ship was capable of spatial dematerialisation, allowing it to disappear from one location and reappear in another (Much like the TARDIS, except that it could not travel in time). Using this technology, Xanxia managed to enhance the equipment so that it could dematerialise an entire planet, subsequently gutting Zanak itself for the energy and mineral wealth needed for the next stage of her plan. Establishing time dams around her original body, Xanxia was able to use a projection system to create a new body based on cells from her old one, the time dams keeping her original body physically alive while allowing her to project her consciousness into the ‘hologram’. With the Captain as her somewhat-unwilling servant while she used a public appearance as his nurse to prevent anyone realising who she really was, Xanxia began a campaign across the galaxy, travelling from world to world by having Zanak materialise around other planets and mine them for their mineral wealth, the local population kept at a certain level of development to prevent them from learning the truth about the universe around them.
As far as the local population were concerned, Zanak’s rule by Xanxia was a thing of the past, and the Captain’s regular announcements of new Golden Ages were relatively common, unaware that the changing lights in the sky meant that they had just travelled to another world and were now destroying it with their automated mining equipment. As the planets’ mineral wealth was used to support Zanak, Xanxia had the energy released by the dying planets sent into the time dams keeping her body frozen, convinced that she would eventually reach a point where the dams had absorbed so much energy that they would allow her new body to become permanent and her old one to die at last. However, she was unaware that the Captain was secretly plotting against her, attributing his decision to collect the remains of the destroyed worlds in a ‘trophy room’ as a harmless opportunity to exercise his old genius due to the complex gravitational balance he had to create so that the compressed mass of the worlds collected would balance each other out without crushing anyone who went to observe the remains. Another interesting side-effect of Zanak’s mining operations was the creation of the Mentiads – telepathic individuals whose powers were enhanced as they absorbed the psychic energy released when the worlds were destroyed , although their inability to understand the Captain or Xanxia’s evil natures limited what the Mentiads could do against them despite their power.
The travels of Zanak continued relatively unabated until they reached the planet Calufrax shortly before the Fourth Doctor, Romana and K9 arrived there, the three currently engaged in their quest for the Key to Time (“The Ribos Operation”), the Tracer having identified Calufrax as the location of the second segment. Confused at the presence of Zanak instead of the ice-planet of Calufrax, The Doctor swiftly befriended Kimus and Mula, the friend and sister respectively of Pralix, the newest ‘recruit’ to the Mentiads, while Romanawas captured by the Captain’s forces and taken to investigate recent damage that Zanak’s engines had suffered as a result of the TARDIS’s materialisation interfering with their own systems. After Romana escaped, The Doctor, Romana, Kimus and Mula met with the Mentiads, a quick investigation of the mines confirming The Doctor’s theories about the true nature of Zanak. Returning to Zanak’s bridge to carry out a closer investigation, the discovery of the time dams containing Xanxia’s body helped The Doctor realise what was happening, deducing the nurse’s true identity as she was the only person the Captain never yelled at.
Although The Doctor was unable to simply turn off the projection of Xanxia’s new body as it had become too corporeal to be turned off, he nevertheless dismissed her plans for immortality as the greatest load of ‘bafflegab’ he’d ever heard in his lives. Even as Xanxia protested that she had calculated everything, The Doctor coldly informed her that the energy needs of the time dams increased exponentially every time she charged them up, and there simply wasn’t enough energy to sustain them forever even if she resorted to trying to drain the energy from suns to support herself. Refusing to accept The Doctor’s claims, Xanxia made plans for the next jump, but the knowledge that Earth was her next target prompted The Doctor to take more drastic action.
Despite the Captain’s use of a special generator that blocked the Mentiads’ abilities – powered by the various mineral samples he’d acquired over the centuries , K9 was able to generate a counter-jamming frequency to help the Mentiads destroy Zanak’s engines while The Doctor and Romana used the TARDIS to slow Zanak’s materialisation. Returning to the trophy room, The Doctor revealed that the Captain had always intended to rebel against Xanxia by using the planets’ gravitational mass to create a standing vortex in the middle of the time field – once he had enough planets to do so – that would cause time to start again inside the field (Unable to simply destroy the field due to the energy release that would have resulted causing an explosion that would have destroyed his entire base), but the plan was flawed as Calufrax, the last planet collected, was actually the second segment of the Key to Time, and hence operated on a different gravitational frequency to the others.
Although the Captain was destroyed when his planned rebellion failed, Xanxia’s new body was subsequently disrupted when Kimus shot her, giving The Doctor the chance to access the Captain’s equipment. Creating a hyper-spatial shield around the shrunken planets, The Doctor linked Zanak’s controls to the TARDIS, allowing him to dematerialise Zanak for a moment and then invert a gravity field at the hyper-spatial force field, dropping the shrunken planets (With the obvious exception of Calufrax) into Zanak’s centre, allowing them to expand and fill the hollow mass that had been left there long ago. With the Captain’s base destroyed and Xanxia dead at last, The Doctor, Romana and K9 departed to collect Calufrax and convert it into the second segment, The Doctor confident that Zanak would be able to make a good existence in this part of the galaxy thanks to its plentiful mineral wealth and interesting neighbours for when they got around to conventional space travel.