Your Dark Materialists analyze Chapters 4 and 5 and find there's much to discuss.
As we begin Chapter 4, The Master has invited several female guests to Jordan College and introduces Lyra to each of them, including a dark haired, elegant young woman named Mrs. Coulter. She asks Lyra to sit next to her at dinner, and it comes up in conversation that Mrs. Coulter knows Lord Asriel and has been to the North several times. Lyra likens this to Mrs. Coulter being an explorer and is completely enamoured by her for the rest of the evening. When the guests leave for the night, The Master asks Lyra to stay behind for a talk. He inquires about Mrs. Coulter and Lyra exclaims that she is the most remarkable person she has ever met. To this the Master sighs, then explains that it is time for Lyra to leave Jordan College. At first, Lyra resists the idea, not wanting to leave her home and friends, but her feelings quickly change when she finds out that she would be going to live with Mrs. Coulter. Early the next morning, Lyra is summoned in secret to the study to meet with the Master before breakfast. He tells Lyra that he has something for her, but she must swear to keep it private, especially from Mrs. Coulter. The Master gives Lyra something like a watch or clock, a thick disc of gold and crystal called an alethiometer. He quickly explains that the alethiometer will tell her the truth, and that she will have to learn to read it on her own, but above all else, he implores her to keep her own counsel. She leaves for London with Mrs. Coulter, remembering about Roger only after saying goodbye to the servants.
London is unlike anything Lyra has ever seen. In stark opposition to the grand, stony walls and rooms of Jordan College, everything in Mrs. Coulter’s flat is fanciful and pretty, delicate and charming. Lyra is swept up by the upscale life of Mrs. Coulter. Six weeks after Lyra arrives, Mrs. Coulter decides to throw a cocktail party. Although she won’t admit it, Lyra is beginning to feel cramped by this luxurious lifestyle and longs to be with her friends in the streets of Oxford. On the afternoon of the cocktail party, Mrs. Coulter asks Lyra to remove a white shoulder bag she is wearing, which Lyra questions because it is where she is keeping the alethiometer. Mrs. Coulter’s daemon pounces on Pantalaimon, hurting him and Lyra as well, until she promises to say and do exactly what Mrs. Coulter asks of her. During the party, Lyra overhears some guests talking about Dust and something called the Oblation Board, of which Mrs. Coulter is a part. Lyra realizes that the Gobblers, who have been taking children, and who have taken Roger, are affiliated with the Board. An older gentleman named Lord Boreal speaks to Lyra and reveals to her that Mrs. Coulter wishes to use her to round up other children. This horrifies her. As she tries to gather her thoughts, she overhears that Lord Asriel has been imprisoned in Svalbard, guarded by the panserbjørn, or armoured bears. Having heard enough, Lyra and Pantalaimon decide to escape from Mrs. Coulter’s house and run away into the city.