It's 1988 and Dexter Mayhew and Emma Morley have only just met. They both know that the next day, after college graduation, they must go their separate ways. But after only one day together, they cannot stop thinking about one another. As the years go by, Dex and Em begin to lead separate lives—lives very different from the people they once dreamed they'd become. And yet, unable to let go of that special something that grabbed onto them that first night, an extraordinary relationship develops between the two.
Over 20 years, snapshots of that relationship are revealed on the same day—July 15th—of each year. Dex and Em face squabbles and fights, hopes and missed opportunities, laughter and tears. And as the true meaning of this one crucial day is revealed, they must come to grips with the nature of love and life itself.