Before the credits, there is footage of a stone circle with a voiceover concerning demon worship and witchcraft over the centuries which still endure today.The film starts with Professor Harrington (Maurice Denham) drving through the night to Lufford Hall, the magnificent residence of Dr. Julian Karswell (Niall MacGinnis) with whom he pleads to "call it off". Karswell, noticing the time, ushers Harrington out and telling him he will do all he can.As he arrives home Harrington hears a strange noise and through the night can see a huge demon approaching. He attempts to drive away but reverses his car in to an electricity pole, staggers out of it and is caught in the sparking cables as the demon reaches down to claw at his body.Cut to the interior of an aeroplane where Dr. Holden (Dana Andrews) is attempting to sleep. Over his face is a newspaper and visible is an article headlined "Prominent Psychologist Flies to London for International Convention" bears his photograph. In the seat behind him is a young woman -- Joanna Harrington (Peggy Cummins).Holden is met at the airport and discusses the convention he is attending with waiting journalists. Meanwhile Joanna Harrington attempts unsuccessfully to telephone Professor Harrington's house.Holden meets up with two of his fellow delegates Professors Mark O'Brien (Liam Redmond) and K.T. Kumar (Peter Elliot). O'Brien and Holden discuss the case of Rand Hobart (Brian Wilde) -- a member of the Karswell "devil cult" which Holden intends to denounce at the conference. Hobart is in a lunatic asylum for murder, although he claims that the killing was done by a demon. Under hypnosis Hobart has produced a drawing of a demon which bears striking similarities to various other drawings of demons produced over the centuries.The telephone rings and it is Karswell, who attempts to warn Holden off.The following morning Holden goes to the reading room of the British Museum, where he discovers that 'The True Discoveries of the Witches and Demons' --- mentioned in Prof. Harrington's notes --- is missing.In the reading room, Karswell approaches him and offers to let Holden use his library of books on witchcraft and demonology --- which includes a copy of 'The True Discoveries of Witches and Demons', inviting him to visit him at Lufford Hall. Karswell gives Holden a card, and "accidentally" upsets the papers on his desk, apologises and hands them back to him. He leaves. Holden looks at the card and finds that as well as karswell's name and address it also has "In memoriam Henry Harrington allowed two weeks" in glowing letters. He watches Karswell walk away and is suddenly overcome with dizziness and blurred vision. He shows the card to an assistant in the library, but the "In memoriam..." text has disappeared. He next takes the card to a chemist (Chalres Lloyd Pack) who can find nothing wrong with the card.Cut to the church in which the funderal of Professor Harrington is being held. Holden and Joanna Harrington recognise each other from the aeroplane. Joanna tells Holden that they must speak and they meet at Holden's hotel that evening. She advises Holden to drop his investigation of the Karswell cult.She reads from her uncle's Diary, where he recounts that Karwell gave him a concert programme which contained a parchment with runes written on it, which acted as if it were alive and flew in to the fire and was burned; and that ever since he has been pursued by strange lights and has had various other signs of the supernatural. The chemist telephones Holden to inform him that the card on which he saw the writing has come back clean: there is no sign of any ink on the card.Holden and Joanna Harrington drive out to Lufford Hall, where they find Karswell performing magic tricks for a group of children. Holden and Karswell talk about 'The True Discoveries of Witches and Demons', which Karswell informs Holden was written in cypher, and that he has de-cyphered. Holden continues to be sceptical, so Karswell offers to conjure a wind-storm. He concentrates for a few seconds and a tremendous storm appears from nowhere.Karswell and Holden run indoors to avoid the storm. Karswell explains to Holden that -- like Prof. Harrington before him -- he has put a curse on him, which will lead to his death three days hence. Meanwhile Karswell's mother (Athene Sayler) is showing Joanna Harrington Karswell's copy of a book (presumably 'The True Discoveries of Witches and Demons'), which neither of them can understand. Holden and Joanna Harrington leave Lufford Hall.Back at the hotel, as Holden walks along the corridor he begins to hear the strange noise which preceded the manifestation of the demon which killed Prof. Harrington but it is interrupted by the door of a room opening. Talking with O'Brien and Kumar, Holden is still sceptical. O'Brien looks in Holden's diary and discovers all the pages after the date which Karswell has arranged for his death have been torn out.Holden has dinner with Joanna at Prof. Harrington's house. Joanna continues to read from her uncle's journal, and Holden discovers that the pages of Prof. Harrington's diary after the date of his death had been torn out. Still sceptical Holden tells Joanna that even if a curse did exist, he couldn't have been subject to it as a paper has to be passed -- secretly -- to the victom of the curse. He goes through the papers in his briefcase and discovers that amongst those returned to him by Karswell in reading room is one bearing a runic script. The paper flies from his hand towards the fire but is stopped by the fire-guard. Holden retrieves it.The following day Holden visits Rand Hobart's -- who are also members of the cult -- family to seek their permission for him to be released from the asylum temporarily to be examined at the conference. Hobart's mother signs the release paper and as he goes to put it in his wallet the runic parchment makes another bid to escape.Holden then arranges to meet Joanna, who has been invited to a seance by Karswell's mother. The seance is run by Mr. Meek (Reginald Beckwith). During the seance, Mr. Meek goes in to a trance and begins to "channel" Prof. Harrington who has a message for Joanna that Karswell has successfully translated the book and that the demon is real. Holden leaves the seance in disgust, still refusing to believe that demons exist. Joanna and Holden decide to drive out to Lufford Hall to try and find Karswell's translation of the book. Holden breaks in to Karwell's study, where he is attacked by what appears to be a wild-cat [more accurately, he wrestles with an evidently stuffed cat -- the effects in this bit are less than convincing]. Karswell appears and the "wild cat" has now assumed the form of an ordinary cat, and Karswell informs Holden that it is a minor demon.Against Karswell's advice, Holden returns to his car through the woods. On his journey he sees huge smoking footprints appear in the path at his side, followed by a strange smoky apparition and the strange noise. They phenomena disappear. Holden and Joanna go to the police who dismiss them as a pair of cranks.The following morning Holden is having breakfast with Kumar and O'Brien. He refuses to accept a call from Karswell's mother who keeps trying to call him. Karswell's mother then telephones Joanna and tells her to tell Holden that Rand Hobart knows how to reverse the curse. Joanna then goes to her car and is about to leave when someone steps out of the bushes and prevents her...Hobart is brought by ambulance to the conference, and Holden explains to the delegates that he and O'Brien will use hypnosis to bring Rand Hobart out of his catatonic state. Hobart is injected by O'Brien with stimulants, and regains consciousness but begins screaming wildly until Holden hypnotises him. Holden shows his runic parchment to the hypnotised Hobart who then he reveals that he was going to be the original victim of the demon, rather than the man of whose murder he is accused. In order to reverse the curse he had secretly to pass the parchment containing the runic inscription back the person who gave it originally. Hobart then breaks free and then dives through a window to his death.Finally convinced of the reality of the curse, Holden decides to return the parchment to Karswell and is informed by Kumar that Mrs. Karswell had told telephoned to say her son would be on the 8.45 to train to Southampton. Holden just catches the train as it pulls out of the platform. As it does so, visible on it are two plain-clothes police-officers. He finds Karswell, who has Joanna with him, whom he has hypnotised.Holden attempts to pass Karswell an envelope containing what he claims to be a retraction. Karswell refuses to take it, fearing it is the runic one. He similarly refuses a cigarette. As the time approaches 10.00 Karswell makes to leave, but Holden insists that he stay to be present when the demon is due to arrive. The police are, however, waiting for him and come in to the carriage and restrain Holden.Karswell makes to leave, and Holden passes his coat to the policeman -- secreting the paper in its pocket. The policeman passes the coat to Karswell who takes it but then instantly realises his error, and pulls the paper out of the pocket. It flies out of his hands and goes dancing down the railway track, with Karswell in pursuit. Holden observes that it is 9.58 ("Two of ten").Just as Karswell reaches the paper it bursts in to flames and is destroyed. The strange noise which preceded the arrival of the Demon at the beginning of the film is heard again, the strange cloud which pursued Holden through the woods also appears above an oncoming train and the demon appears and destroys Karswell.The police and railway staff rush to see what has happened, and even though he is lying onthe wrong track that a train must have hit him and dragged him due to the mutilation of the body. Holden and Joanna refuse to look because "it's better not to know".The end.
Output: Question: who telephones joanna?, Answer: Karswell's mother