45 Years begins on a Monday, commencing a five-day countdown before Geoff (Courtenay) and Kate (Rampling) are to celebrate their sapphire anniversary. These childless retirees -- she was a schoolteacher, he worked as a manager at a local plant -- still have tremendous affection for each other. But her enthusiasm for the commemoration, and her long-held confidence in the relationship itself, is destabilized by news regarding Geoff's previous love, Katya, who died in a hiking accident in 1962.
Haigh's movie is told through Kate's point of view, that of a woman whose confidence in her union, and maybe even in herself, is completely upended by an all-consuming jealousy about her husband's past and a ghost she never knew. "I can hardly be cross with something that happened before we existed, can I?" she tells Geoff after learning more about Katya, her logical, serene response belied by the two words she utters next: "But still." As Geoff grows wistful about this pre-Kate era, his devoted spouse's sleuthing becomes more masochistic. When she comes across a particularly devastating clue, Rampling makes the moment even more potent through her barely audible gasps: Kate's quietly quickened breathing signals her determination not to give in to histrionics, no matter how much she may be reeling.