As the Fifth Doctor and his companions vacation in Tasmania they become caught up in a scheme by the Time Lord Ruath to resurrect the vampire Yarven (from Blood Harvest).

Nyssa, while trying fight her new vampire nature, is drawn to Yarven's castle, where she learns more about Ruath's plan.

Ruath has created a genetically enhanced mist that can turn normal humans into vampires, and kill those who use traditional methods (garlic, crosses, etc.)

[1] The back cover of Goth Opera says that it takes place between the television stories Snakedance and Mawdryn Undead.

The artwork had to be adjusted and the blood airbrushed out when retailer W H Smith insisted that they would not stock the book in that form.