As Kate prepares for her 45th wedding anniversary, her husband Geoff receives a piece of news that takes him back in time: the body of his girlfriend, who died in an accident in the Swiss Alps 50 years ago, has been found. Kate and Geoff are both shaken but unable to communicate their deepest insecurities. Geoff shuts himself off in a world of memories, while Kate tries to suppress her jealousy and anxiety as she prepares for the party, arranging music, menus and the like. On the surface, everything seems normal, but the camera keenly captures the process of the originally harmonious coexistence gradually becoming unbalanced. Whether having breakfast with Geoff or walking alone in the town, Kate feels more and more like a stranger. The couple in "45 Years" are seized by unexpected emotions and forced to face unfamiliar feelings. In the process, their good times seem to be gone forever. After living together for 45 years, which emotion will prevail on their wedding anniversary?