Having lived abroad for many years, Rosie decides that it's time to return to Dublin to look after her ageing aunt Min. Nothing much has changed in the area where Rosie grew up, and Min’s increasing lack of interest in life begins to sap Rosie’s spirit. While flicking through some self-help books looking for ways to distract Min, Rosie gets the idea to write an inspirational book for the middle-aged. Since her only contact in the world of publishing is her friend Markey who lives in New York, Rosie decides to put Min in a temporary care home while she travels to the United States to seek Markey's advice.

Rosie is stunned when Min flees the home and follows her to New York. Suddenly the roles are reversed: Min, having no desire to return to her old life in Ireland, is energised by her new surroundings and sets off on a series of bizarre adventures. And so Rosie, who craves a reconnection with her roots, returns home alone to continue working on her book, which becomes ever more complicated as Markey tries to persuade her to drastically rethink her approach. Suddenly Rosie finds herself on a very different journey of self-discovery, at once painful and exhilarating, yet lucid and humorous, as she confronts her own reality: family, friendship and love, and the passing of time.

Best Love, Rosie is the warm and heartfelt story of two women who passionately resist the notion that there is a right age for everything.