Grant (Pinsent) and Fiona (Christie) are a retired married couple living in rural Brant County, Ontario. Fiona begins to lose her memory, and it becomes apparent she suffers from Alzheimer's disease. Throughout the film, Grant's reflections on his marriage are woven with his reflections on his own infidelities, and influence his eventual decisions regarding Fiona's happiness.
When she feels she is becoming a risk to herself, Fiona decides to check into a nursing home, where one of the rules is that a patient can not have any visitors for the first 30 days, in order to "adjust". Wary of this policy, Grant agrees anyway, at the insistence of his wife whom he loves. During the drive to the facility, Fiona acknowledges Grant's past infidelity while he was a university professor. Despite the awkward situation, the couple makes love one last time before separating.
When the 30 day period ends, Grant goes to visit his wife again, only to find she has forgotten him, and turned her affections to Aubrey (Murphy), a mute man in a wheelchair who has become her "coping partner" in the facility.
While seeing his wife grow closer to Aubrey, Grant becomes an unhappy voyeur when visiting his wife at the nursing home. As time goes by and Fiona still does not remember him, Grant even wonders whether Fiona's dementia is an act meant to punish him for his past indiscretions. After some time, Aubrey's wife removes him from the home due to financial difficulties. This causes Fiona to sink into a deep depression, with her physical wellbeing also appearing to deteriorate. Grant is touched by this, and visits Aubreys wife Marian (Dukakis) in an effort to allow Fiona to see Aubrey again. He would rather see his wife happy with another man than miserable and alone. Marian initially refuses, but the meeting leads to a tentative relationship between her and Grant.
As time passes, Grant continues to visit both Fiona and Marian. He eventually moves out of his home and succeeds in taking Aubrey back to visit his wife. But in his "moment alone" before he brings Aubrey into Fiona's room, Fiona temporarily remembers him and the love she has for him. The film closes on their embrace.