The film follows Angus Flint (Peter Capaldi), a Scottish archaeologist who discovers a strange skull on the site of an old convent. Believing the skull belongs to the d'Ampton Worm, a legendary snakelike creature thought to be slain by the ancestor of local landowner James d'Ampton (Hugh Grant), Angus soon finds himself in danger as a spate of disappearances leads him to think that the evil creature may have returned from the dead to terrorise the locals once more.