It's 1988 and Dexter Mayhew and Emma Morley have only just met on the night of their graduation. Tomorrow they must go their separate ways. But after only one day together, they cannot stop thinking about one another.

Over twenty 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.