Thursday is a Seattle-based nurse who shares her husband, Seth, with two other women in a plural marriage arrangement. Haunted by a recent miscarriage and emergency hysterectomy, she struggles with intense feelings of inadequacy regarding the other wives. Her desperate need to maintain appearances and be the perfect spouse drives her obsessive curiosity about the women she shares Seth with.

Seth is a charismatic contractor who splits his time between Seattle and Portland to maintain a plural marriage with three different women. Growing up in Utah within a polygamist family, he holds strong desires for biological children, which dictates his relationship dynamics. He demands total compliance with the strict rules of his marriage arrangement and exhibits a controlling temper when his wives ask questions.

Regina is a successful Portland-based lawyer and Seth's first wife, initially known to Thursday only as "Tuesday." She prioritizes her career over domestic expectations, making her a stark contrast to Thursday's traditional view of a spouse. Her independence and professional drive create a distinct dynamic in Seth's plural arrangement.

Hannah is a freelance photographer and Seth's newest wife, originally referred to by Thursday as "Monday." Young, beautiful, and currently pregnant, she represents everything Thursday feels she cannot provide for their husband. She maintains a picturesque home and initially appears to live an idyllic, perfect life.

Lauren is a young nurse working alongside Thursday in Seattle. She presents the image of a flawless life, constantly sharing stories and photos of her travels with her husband. Behind her carefully constructed public facade, she struggles with profound marital issues and feelings of inadequacy.

Dr. Steinbridge is a consulting physician at Queens County hospital. He attempts to help Thursday process the reality of her physical and psychological trauma while managing her complex family dynamic.

Thursday's mother is a traditional woman who firmly believes a wife's primary duty is to her husband and household. She frequently pressures her daughter to adhere to strict gender roles, unknowingly exacerbating Thursday's deep-seated insecurities about her marriage.

Thursday's father is a distant patriarch who highly values the illusion of perfection. He holds strict traditional views on gender, believing men should work while women manage the home, a philosophy that deeply influences his daughter's worldview.

Debbie is a nurse who works with Thursday. She casually admits to checking up on her husband's ex-girlfriends, normalizing the type of obsessive behavior that Thursday secretly engages in.

Susan is a young woman who becomes Thursday's roommate in the psychiatric ward. She was admitted after having a severe reaction to discovering her husband's infidelity.