Raised by "spiteful, tormenting" parents, Isobel herself is not particularly likable. Fear, guilt, and anger—her most common emotions—have warped her development, and she's only happy when she's reading. Isobel is guarded and watchful around people her own age. Though she wants to fit in, she's baffled by their speech and behavior, which seem utterly foreign to her. When Isobel realizes that mortality links all humans—and that a childhood trauma about her poetry was based on her parents' lies—she can finally move forward.
May Callaghan is a monstrous person. The rare glimpses of kindness she displays are as inexplicable as her viciousness, and the only possible excuse for her behavior would be that she's mentally ill. She favors her daughter Margaret over Isobel—but she isn't especially kind to Margaret either. As Isobel realizes, her mother is energized when Isobel reacts to her mother's rage. She is verbally and physically abusive toward her children, denying Isobel from even experiencing the joy of a childhood birthday. Her abusive nature sets Isobel up for failure in childhood and prohibits her from following her true passion, writing. She dies when Isobel is 18.
Unlike Isobel, Margaret has mostly submitted in the face of their mother's bizarre behavior. Margaret gets presents for her birthday. She imitates her mother's genteel speech and avoids punishment. Margaret also gets to participate in the school play, something Isobel would never be allowed. But on some level, Margaret knows her mother is sick and refuses to put up with the sickness. When she sharply defends her right to keep a drawer for private possessions, Mrs. Callaghan cowers with fear. After the play, Margaret no longer tries to please her mother. She has found friends her own age.
Aunt Noelene is the closest thing Isobel has to a mother. She pays for Isobel's business college, buys her clothes for the office, and gives her spending money. She tries to give her niece advice as well, but Isobel barely understands what she's being told. Aunt Noelene is perceptive about Isobel's unworldliness but also perplexed by it. She doesn't seem to love Isobel, but she does want to give her a good start in life.
Since readers see Mrs. Bowers through Isobel's eyes, and since being a landlady is not a fun job, it's not easy to assess her character. She speaks sullenly and doesn't seem to get much out of life, but she saves Isobel's dessert on the nights she's out for dinner. She disapproves of sex and marriage, seeing both as an imposition on females.
Although Diana's appearances in the book are brief, she makes an outsized impression on the reader. Diana is the victim of emotions that were forced on her when Nick left her. She's abjectly miserable over the breakup; just saying Nick's name makes her cry. She knows he hates her for stalking him; she knows stalking him is useless and is ashamed of herself, but she can't make herself stop. Yet Isobel's counsel makes enough of an impression on Diana that when she hears Nick is dead, she doesn't grieve. His death enables her to move on.
Although Mrs. Adams plays a small role in the novel—she does not enter the present-day story until Chapter 5—her influence on Isobel's life is huge. Her kind interaction with Isobel, in which she praises the childhood poem Isobel wrote about Mrs. Adams's cat, both shows Isobel how cruel her parents were and rekindles Isobel's desire to write.