Ruth is a 30-year-old sonography technician who returns to her California hometown feeling adrift after her fiancé ends their engagement. She decides to stay for a year to help care for her father, who is showing early signs of Alzheimer's disease. As she readjusts to her childhood home, she channels her energy into cooking meals that promote brain health and trying to reconstruct a meaningful life.

Howard is a history professor who recently lost his university position due to early-onset Alzheimer's disease. He is deeply loved by his family but carries a history of alcohol misuse and infidelity that caused past rifts. Despite his declining memory and occasional bursts of frustration, he maintains a sharp wit and a profound love for his children, often expressing his feelings through old diary entries.

Annie is Ruth's mother, a resilient woman who was adopted from China as an infant and lost her adoptive parents young. Once known for making everything from scratch, she has recently stopped cooking out of a fear that aluminum cookware caused her husband's illness. She stoically bears the burden of Howard's care while holding onto painful memories of his past mistakes.

Linus is Ruth's younger brother by five years, who currently lives in Santa Cruz. Because he lived at home during their father's period of heavy drinking and infidelity, he harbors significant resentment toward Howard and initially refuses to visit. He struggles to balance his love for his mother with his anger toward his father.

Theo is Howard's loyal and proactive teaching assistant. Recognizing how much Howard misses teaching, he takes the initiative to organize a covert, unofficial class with former students to keep the older man's mind occupied. He becomes a steady, supportive presence in Ruth's life as she adjusts to being home.

Joel is Ruth's former fiancé, whom she followed across the country during his medical school residency. He recently ended their relationship after admitting to an affair, packing his things separately and leaving Ruth to figure out her next steps alone.

Bonnie is Ruth's childhood best friend, who is half-Armenian. The two lost touch while Ruth lived in Connecticut with Joel, but they quickly rekindle their bond when Ruth returns to California, offering Ruth a social outlet away from her family's stress.

Joan is a former student of Howard's who participates in the fake class organized by Theo. She displays a noticeable eagerness to catch Howard's eye and assist him, prompting Ruth to question the nature of her past relationship with her father.

Dean Levin is an administrator at the college where Howard taught. He has a long-standing rivalry with Howard, culminating in his decision to fire him due to his worsening memory symptoms and erratic behavior.

Uncle John is Howard's brother, who provides a lighter, more humorous presence for the family. He checks in on the Young family frequently and shares fond memories of Annie and Howard from before the illness took hold.

Maxine is a medical doctor and friend of Ruth's from San Francisco. They bonded when Maxine found Ruth crying at work near the end of her relationship with Joel, and she consistently offers Ruth practical life advice.

Dr. Nazaryan is Bonnie's father and a professor at the same college as Howard. He is eager to support the plan to keep Howard occupied and generously offers his own classroom for their secret meetings.

Carl is an eccentric truck driver who crosses paths with Ruth on her drive back from Santa Cruz. He gifts her a homemade recipe book filled with endive recipes, sharing a philosophy about leaving things behind to be remembered.

Deb is an old high school friend of Ruth's who now has children. After their chance meeting, she begins sending Ruth enthusiastic chain emails containing recipes for microwave mug cakes.

Vince is Bonnie's current boyfriend, whose slightly strange demeanor and questionable comments prompt Ruth to silently judge him, though she keeps her thoughts to herself for Bonnie's sake.

Kristen is the woman involved in the end of Joel and Ruth's engagement. She moves to Charleston with Joel to start a new life together, remaining an off-page source of insecurity for Ruth.

Rita is a flight attendant and Linus's girlfriend. Linus worries they have nothing in common after she returns from a long trip to Bali.