The legend dates back to Roman times, at least: a great White Worm, as wide as a man, slithers out of the rocks of the Dark Peak Gap to take animals, sometimes even children, for its food. When the Doctor and Leela arrive in the wilds of Derbyshire, only to get caught up in the hunt for a missing girl, they soon discover that the legend of the Worm is very much alive – even now, in 1979. Worse still, it seems that the Doctor isn't the only renegade Time Lord on the trail of this deadly and mysterious Worm...