Ragnar Pole, an unmarried writer of 39 who is "read by few, comprehended by fewer, wanted by none", arrives late to a social soiree at the home of Lois and Felix Wayland, in time to hear the playing of Beethoven's Opus 31, No 3. Here, he meets his brother Waldo's wife, Adrienne, and is invited to stay with the couple at their cottage in Swayning, Sussex. Adrienne and Waldo are experiencing some difficulties in their marriage, and she hopes Ragnar might have words with his younger brother. Adrienne then tells him that the woman playing the piano, Cecilie Toller, also lives in Swayning, and has with her at present two unusual, musical guests, the famous violinist Marya Klangst, and a mysterious young woman called Urda Noett, whom Adrienne urges him to meet.
Ragnar moves on to greet his hostess, Lois Wayland, who tells him that her husband, working in his study upstairs, wants to talk. Before he can leave the party, however, Ragnar encounters a young woman, Faustine Gaspary, in a distressed state. She says that "Something is wrong here this evening," something she links with the presence of Urda Noett. "I assure you," Faustine says, "she is a witch."
Upstairs, Felix Wayland puts forward a proposal. His journal, Memnon, is not doing well — something for which he blames such popular distractions as the radio, and the current trend in journalism for pleasing "the proletariat" who want "above everything to be immediately fascinated" rather than to read material of any worth. He wants some cash investment to see him through this lean period, but Ragnar cuts short the meeting because of a growing distraction, which he associates with Urda Noett, still unseen in the room below. Felix says that a man going by the singular name Bluewright is coming to the party with the intention of talking to Ragnar, and Ragnar goes back downstairs, after having arranged a further meeting with Felix for the next day. In the room below, Ragnar sees Urda Noett and Bluewright, then immediately realises he is not seeing them, but a twin apparition, as the two almost instantly disappear. He is told that Urda has already left the party, and that Bluewright never turned up.
At home the following evening, Ragnar receives a letter from Bluewright. It relates a dream in which Bluewright seems to be endlessly travelling through the rooms of an enormous house. Something about the dream and certain passages in Ragnar's written works has convinced Bluewright that this house actually exists. Bluewright says he would like to meet with Ragnar to discuss this. Shortly after reading it, the letter disappears.
Gaspary (Faustine's father) is staying at Ragnar's house that night. Something of an expert on occult matters, he talks about witches throughout history, then discusses Ragnar's hallucination at the Waylands'. The next day, Ragnar accompanies Gaspary to his home at Leigh, where they find Cecilie Toller in conversation with Faustine. Cecilie has invited Faustine down to her house in Swayning, but Faustine is reluctant to agree. When Cecilie leaves, Ragnar talks to Faustine alone, and she reveals that she has had a dream about him entering a mysterious, supernatural house, a house she identifies with Urda Noett. Faustine, who claims to be psychic, feels that Urda Noett is drawing Ragnar into a meeting in which he will be given a vision of heaven — but this, she says, is something that ought not to be given to living men. Ragnar, however, says he cannot pass up such an opportunity, and decides on a compromise: he will go to see Urda in Faustine's company, and, rather than waiting for the appointed time, proposes to travel to Swayning the next day for a surprise visit.
That afternoon, walking in the countryside, Ragnar pauses at an inn in an out-of-the-way village, and there encounters an old school acquaintance, a folklorist called Flint, whom Ragnar had thought to be dead. He asks Flint about the possible origins of the name Bluewright — whom Ragnar is beginning to think is not a real person, but some sort of supernatural being — and is told of an area of land called Bloodwedswyrht, and a Morion House that once stood there, both associated since ancient times with witches. When Flint reveals that he has found this place, and that it is near Swayning, Ragnar realises this is one more fateful call drawing him to Urda Noett.
As if more were needed, that evening Ragnar's brother Waldo appears. He tells of a visit he tried to pay to Urda, and how he was refused entry to the house as he was not the "expected" Mr Pole. Lingering outside, Waldo saw a peculiar vision of a waiting man who turns into a "black gap", a "fissure of darkness" — and who Ragnar guesses is Bluewright, a figure now gaining an aura of death about him.
Ragnar and Faustine travel to Urda Noet's house. They are told Urda is out walking. Ragnar is invited in, while Faustine waits outside. Being taken to see Mme Klangst, Ragnar finds himself walking, not through the interior of a house, but through a dark, external landscape. Inexplicably, he finds himself outside again, walking with Faustine to where they might meet Urda. The two have an intense discussion about whether what Ragnar is doing is spiritually right. This comes to an abrupt end when they happen upon a second house where Urda waits.
At this point the narrative turns into a long description of how Ragnar comprehends the true nature of reality, a vision that comes to him as soon as he sees Urda in the doorway of the house. It seems to him that the only realities of the world are pain and loneliness; love, the supposed antidote to these things, is not the ultimate answer because pain always returns, pain alone leads to self-knowledge, and love could not exist save against a background of loneliness. Life — even the life of the soul in heaven — must, then, be nothing but a series of deaths, each death stripping away more and more of the self until only the impersonal spirit remains, a spirit that can be at one, once more, with the Ancient from which it once issued. But this oneness can never occur within the bounds of life or time.
This published portion of The Witch ends with Ragnar on the verge of entering Urda Noet's house.