Mrs. Coulter invites Lyra to sit next to her at dinner. Lyra is entranced; she's never seen a woman like her before. She tells Mrs. Coulter everything about her life and ignores the other dinner guests. After the meal, one woman asks Lyra if the Scholars are going to send her to school. Blankly, Lyra says no. She says that Lord Asriel promised to take her to the North next time he goes, and Mrs. Coulter says that he told her this too. Mrs. Coulter goes on to say that she's here because of Lord Asriel, whom she met at the Royal Arctic Institute while studying the Aurora. Lyra is then even more interested in Mrs. Coulter.
Lyra's interest in Mrs. Coulter shows how even a perceptive and sharp child like Lyra can be easily manipulated into following someone who does awful things. It's worth noting, however, that Lyra is somehow connected to the upper classes, which means that she's likely safe from whatever the General Oblation Board is doing. Unlike the poor children and the gyptians, Lyra is likely seen as more valuable.
As the guests leave, the Master sends Lyra to his study so they can speak. They discuss Mrs. Coulter and Lyra deems the woman wonderful. The Master looks older than usual, and Lyra realizes that soon, he'll be buried in the crypt with the other Masters. With a sigh, the Master says that Lyra has been safe in Jordan, but it's now time to leave Jordan College. Lyra insists that she wants to stay at Jordan forever and glowers when the Master says that Lyra needs female company—to Lyra, this means boring, smelly female Scholars. The Master asks if Lyra would like to live with Mrs. Coulter, though, and Lyra immediately perks up. The Master invites Mrs. Coulter into the study, and Mrs. Coulter asks Lyra if she's ready to be her assistant and to go North. Lyra is speechless.
Lyra's realization that the Master is getting old is a sign of maturity. She has these moments throughout the novel, and they make it clear that growing up and gaining maturity aren't linear processes; it's possible to have these moments where Lyra is fully aware of her place in the world and others' mortality, and then move on to telling childish lies and being drawn in by Mrs. Coulter's glamour.
Mrs. Lonsdale wakes Lyra before dark the next morning and sends her to knock on the Master's window before she leaves with Mrs. Coulter. The Master lets Lyra in and Lyra asks if she's still leaving. Oddly, the Master says that he can't keep Lyra from going. He then gives her a strange compass in a velvet case and says she needs to keep it private. It's called an alethiometer, he says, and it tells the truth. The Master begins to say something about Lord Asriel, but he stops when someone knocks on his door.
The Master's wording lets the reader in on the fact that he doesn't want to let Lyra go with Mrs. Coulter, something that Lyra doesn't pick up on because she's both confused and excited. Giving her the alethiometer also muddies things, as asking her to keep it private suggests that Mrs. Coulter isn't trustworthy—an idea that Lyra's admiration won't allow at this point.
Lyra only remembers that Roger is missing after she says goodbye to the servants. She feels guilty, but reasons that Mrs. Coulter will be able to help her look for him. In the zeppelin, Pan sits on Lyra's lap as an ermine and stares out the window while Mrs. Coulter talks about how wonderful London is. When they get to Mrs. Coulter's flat, Lyra is in awe: she's never seen anything so pretty. Mrs. Coulter shows Lyra to a lavish bathroom with pink soap and Lyra and Pan play in the bubbles. Lyra remembers the alethiometer in her coat pocket and feels confused, as she promised to keep it secret, but Mrs. Coulter seems kind—while the Master tried to poison Lord Asriel.
Lyra's attempt to figure out where her loyalties lie speaks to her youth again. It also reminds the reader that though Lyra is a child, she's already very caught up in the adult politics of the wider world and will soon need to learn how to navigate those politics. In order to do this, Lyra will need to learn to trust herself and to evaluate the adults around her in a way that she's still unwilling to do.
Mrs. Coulter takes Lyra to the Royal Arctic Institute for lunch and points out other notable members. As they eat calves' liver, she shares that bear liver is poisonous. They look at relics in the library and then go shopping. This is an entirely new experience for Lyra. The clothes are pretty and trying them on is exhilarating. Back at the flat, Lyra takes another bath and Mrs. Coulter comes in to wash Lyra's hair. Pan watches with curiosity until Mrs. Coulter glares at him, and then he modestly turns away like the golden monkey. This is the first time he has to look away from Lyra. Then, Lyra puts on her new nightdress and climbs into the softest bed she's ever slept in.
Making Pan look away from Lyra's body in the bath is a major indicator that Lyra is quickly approaching puberty, but it also suggests that Mrs. Coulter doesn't espouse being wholly open and at ease with oneself. When considered in terms of the way the novel later explains how original sin came to be, this makes sense: gaining experience as one approaches adulthood, it suggests, means experiencing shame about one's body, which not being open with one's dæmon could represent. (This also connects to the biblical Adam and Eve story, which is mentioned later in this book as well—when Adam and Eve ate the forbidden fruit, they suddenly became ashamed of their nakedness for the first time.)
Once Mrs. Coulter is gone, Pan pulls at Lyra's hair and they take out the alethiometer. It has needles pointing in different directions, small painted pictures, and three wheels. Lyra makes the three short needles point at different pictures, but she can't control the fourth. They wonder if Lyra is supposed to take it to Lord Asriel, but Mrs. Coulter interrupts their conversation to tell Lyra to go to bed.
Here, Lyra's inability to work the alethiometer speaks to the simplicity of the world she is used to. While the object more broadly represents Lyra's innocence, in this case it suggests that she needs a bit more experience in order to be able to properly ascertain what the truth is.