The Doctor needs to stop Adric from siding with Monarch and get Bigon quietly restored (who was mechanically lobotomized for previously siding with the Doctor). The ship then gets turned into one big multi-cultural dance party so the Doctor can make a desperate leap for the TARDIS, floating just outside the spaceship, and stop Monarch's plans for Earth. Written by
Did You Know?
Nyssa's sudden fainting spell at the end of the story was a throwback to the style of serial transition often employed during the First Doctor era. In this case, the reason for Nyssa's sudden collapse is revealed at the start of Doctor Who: Kinda: Part One
(1982). See more