Eighteen-year-old Ava Luna puts her future on hold to care for her mother in the days leading up to a risky surgery. Coinciding with the seasons and cycles of the moon, the four parts of this novel tackle family dynamics and mental and physical health as it follows Ava Luna's quest for independence, assertiveness, and wholeness.

Writing in her journal, Ava Luna tries to make sense of her life. Her parents split when she was 13 in a bitter divorce that tore the family apart. She comforted herself by creating her own story for why they could no longer be together, where she likened her mom to the moon and her dad to the sun. In this delicate and magical tale, Mama Moon and Papa Sun are independent forces that remain separate, but can briefly exist together in harmony. As her mom's surgery looms, Ava Luna sees the cycle begin once more as her dad lends his support, and her brother, Ray, sets his resentments aside and they start feeling like a normal family again. Adding to Ava Luna's renewed hope, she has secretly rekindled a relationship with a past boyfriend, Sol, at the weekly contra dance her parents attended when they dated. She hopes this period of alignment will last forever.

Tensions mount when her mom is not recovering as planned and deep-seated resentments amongst Ava Luna's family come bubbling to the surface. She tries to hold the remnants of her family together, but a breach of trust threatens to cause a permanent rift between everyone. Ava Luna runs away in an attempt to find clarity from the moon, the ocean, a psychic, and her lingering lost love, only to find the answers in an unexpected place: herself.