Previously on Doctor Who, the Doctor took a nasty spill from disconnecting the Pharos Project's power cable, prompting his fourth regeneration. Unfortunately, the regeneration is in danger of failing. That is, unless he can get some rest and healing in the TARDIS' Zero Room. Tegan and Nyssa put their heads together (as usual, Adric is being difficult and (unwillingly) in league with the villain), consult the TARDIS manual and inexpertly steer it to "Castrovalva: the Dwellings of Simplicity". Its brochure makes it sound like an alien day spa; the perfect place for a bit of R&R. Watch it here