London, 1967: while the capital comes alive with the new youth revolution, the suburban Fischer family seems to belong to an older world of conventional stability. Homemaker Phyllis is married to Roger, a devoted father with a career in the Foreign Office. Their children are Colette, a bookish teenager, and Hugh, the golden boy. But when the twenty-something son of an old friend pays the Fischers a visit one hot summer evening, and kisses Phyllis in the dark garden after dinner, something in her catches fire. Newly awake to the world, Phyllis makes a choice that defies all expectations of her as a wife and a mother.