Botoya

Botoya was a moon of Gallifrey. Early in Gallifrey's temporal history, the ancients of Gallifrey built into the moon a device that could rewrite history of a large scale before hiding the planetoid. The Doctor suspected that their motivation for doing so was the fear that the device could be misused. The lost moon was unknowingly found, at a point in its timeline where it had decayed into a lifeless asteroid, given the new name "Primeline 275". In Gallifreyan culture, Botoya became a myth, one not widely believed in. Nonetheless a "parable" in the The Book of Rassilon spoke of the moon and its capabilities.

Gostak became obsessed with finding the moon, naming himself as "The Pilgrim" and taking a TARDIS in his quest. Gostak eventually found the moon and had hoped to use its powers to bring about an unending Time Lord Empire. His meddling with Botoya was observed by the nearby Vakrass, last of the Death Lords. Recognising the writing on Botoya as Old High Gallifreyan, Vakrass sought out the Time Lords for aid only for them to give him the means to contact the Doctor. To that end, Vakrass gathered the Fifth, Sixth and Eighth Doctors, each of whom had found a piece of Botoya's chroni-core, to stop their old tutor.

Uniting the three shards of chroni-core formed a portal to Botoya's past, the Doctors stepping through and meeting Gostak. As Botoya needed four Time Lords to operate, Gostak welcomed the three Doctors before activating the device, hoping the danger of its energy running wild would convince them to help. When Vakrass, Vislor Turlough, Constance Clarke and Charlotte Pollard arrived, Gostak threatened them. Though pretending to agree, the Doctors took the chance to turn Botoya's temporal energy inward, being the catalyst for it to become the dead asteroid of Primeline-275. As the moon entered its death throes, the Seventh Doctor arrived with the chroni-core's control plinth, allowing him to evacuate all but Gostak, who refused to leave, and Vakrass, who stayed behind to ensure that Gostak died, though the Doctors were convinced that Vakrass had survived. (AUDIO: The End of the Beginning)