The book leaps out at her in the bookstore: a diamond-studded Puerto Rico constellation gracing a black vellum cover, with an enigmatic name - M. Domínguez - in the lower right-hand corner. For Tatum Vega, out of place at a prestigious East Coast college, it is a lifeline. She writes her first piece of fan mail to the author. When he writes back, she finds herself drawn into an all-consuming and undefinable relationship with the older, charismatic Domínguez.

Over a decade later, Tatum has constructed a new life for herself, but when a reporter contacts her out the blue, this careful separation from her former existence crumbles. Domínguez has been accused of assault by another woman, and the reporter is looking for corroboration. Searching for clarity, Tatum decides to tell her story in a different way: in the form of a letter to Domínguez, recounting and reclaiming the totality of their decades-long relationship from the day they met to the shocking night it all imploded.