Middle aged Oxford housewife Maddie Laurie and accountant husband Malcolm dine with Malcolm's close friend Jack Burrows, an obstetrician, and his new wife Angela. During the meal, Maddie becomes ill and through a series of memories recalls a recent train trip with her son Neil, a university student. On the train, Maddie notices a strange taste in her food and is felled by a sudden seizure after gazing at flashes of light through the windows. She extracts a promise from Neil to keep her "fit" a secret from Malcolm on the proviso she agrees to see a doctor.