Novelist Maurice Bendrix narrates the film as he begins a book with the line "This is a diary of hate". On a rainy London night in 1946, Bendrix has a chance meeting with Henry Miles, husband of his former mistress Sarah, who abruptly ended their affair two years before. Bendrix's obsession with Sarah is rekindled: he succumbs to his own jealousy and works his way back into her life. As the story unfolds in 1946, we also see flashbacks of Bendrix with Sarah as they began their affair during World War II. Henry tells Bendrix that he believes Sarah is having an affair, so Bendrix hires the bumbling but amiable Mr. Parkis, who uses his young birthmarked son Lance to investigate. Sarah asks Bendrix to meet to talk about Henry and the cold tentativeness of their interaction is contrasted with the passion of their earlier encounters. Bendrix learns from Parkis that Sarah has been making regular visits to a priest named Father Richard Smythe under the guise of false dentist visits and he grows increasingly jealous. Flashbacks show Bendrix expressing jealousy of Henry and asking Sarah to leave him. Though Sarah and Bendrix express love to each other, the affair ends abruptly when a V-1 flying bomb explodes near Bendrix's building as he is out in the hallway. Bendrix falls down a staircase and awakes later, bloodied but not seriously hurt. He walks upstairs, where Sarah is shocked that he is alive. Bendrix accuses Sarah of being disappointed that he survived and she leaves, telling him "Love doesn't end, just because we don't see each other". In 1946, Parkis obtains Sarah's diary and passes it on to Bendrix; it shows the affair from her perspective. After Bendrix is hurt by the bomb, Sarah runs downstairs and finds him still and not breathing. After trying to revive him, she runs back upstairs and begins to pray for Bendrix's life. Just as she says to God that she will stop seeing Bendrix if he is brought back, Bendrix comes into the room. Now knowing why Sarah ended the affair, Bendrix follows Sarah and begs her to reconsider. Sarah tells Bendrix that she has felt dead without him and can no longer keep her "promise" to God. Henry, who has figured out that it is Bendrix who was Sarah's lover, desperately asks Sarah not to leave him but, with more persuasion from Bendrix, Sarah agrees to go away with him for a weekend. Henry tracks the couple down to tell them that Sarah has a terminal illness. Bendrix stays with Henry and Sarah over her final days and at her funeral, Parkis tells Bendrix that a chance encounter with Sarah cured his son of his birthmark. At Henry and Sarah's house, Bendrix completes his book and it is revealed that his diary of hate is directed toward God. While Sarah doesn't need to see God to love Him, Bendrix prays God will leave him alone, thereby finally acknowledging His existence.
later used "Diary of Love" to open and close his solo album, The Piano Sings. As with many of Nyman's 1990s scores, he incorporates material from his String Quartet No.3, which was in turn based on a choral piece titled Out of the Ruins.
Track listing
Diary of Hate 2:38
Henry 1:46
The First Time 2:16
Vigo Passage 1:04
Jealous of the Rain 5:29
The Party in Question 3:45
Intimacy 3:04
Smythe with a "Y" 1:55
Dispossessed 3:22
Love Doesn't End 4:31
Diary of Love 5:16
Breaking the Spell 1:20
I Know your voice, Sarah 4:10
Sarah dies 3:01
The End of the Affair 2:59
A contemporary recording of "Haunted Heart" by Jo Stafford is heard in the background during several scenes and the closing credits.
