Doctor Who has always leaned heavily on the Time rather than Space parts of the TARDIS's capabilities, mainly because it meant they could reuse old sets from costume dramas of the sort the BBC adores so. Often the fun comes from putting an alternate history twist on a familiar time period or event as was so with Underworld. Written by Barbara Clegg for Peter Davison's third year on the show, the episode involved the Fifth Doctor in Ancient Greece. Investigating reports of young women being abducted by black tentacles sprouting from the ground, The Doctor takes a trip down the mythical River Styx and discovers a hidden alien race called the Hadeans. Like Hades, get it? It transpires that the reason these aliens have been kidnapping all of the women of a certain age in Greece is because the female Hadeans are infertile. So, um, they need them to carry on their species. Thankfully, The Doctor offers advice on genetics. Can't think what didn't make for suitable tea-time telly there...