The Stranger (Colin Baker) arrives on Earth with no memory of who he is or why he's there. However, two men on a secret mission seem to know his identity and the owner of a local bar/club seems to be hiding a secret in an upstairs room. Unsure of whom to trust or even believe, The Stranger must try and unravel the threads of his mysterious past...a past he may not want to remember.

A henchman of Satan poses as a priest in order to get closer to young virgins he needs for human sacrifice.

维基：

This season introduced K9 to the series and saw the departure of Leela. It was originally intended to include Terrance Dicks' story The Vampire Mutations but, due to a major BBC production of Dracula, it was postponed. It later became Season 18's State of Decay. To replace it, Dicks quickly scripted the season opener, Horror of Fang Rock. The season took a two week transmission break over the 1977 Christmas period, between the broadcast of part four of The Sun Makers and part one of Underworld.