In the afternoon light, the Malfoys make a lovely family portrait. The whole family looks regal, stately, and reasonably content. Happiness is, after all, beneath them. Perhaps that explains why no one smiles.
Astoria Malfoy is the picture-perfect Pureblood wife. She smiles, she engages with guests, she raises her son to be seen and not heard.
Lucius Malfoy is the picture-perfect Pureblood patriarch. He is dignified, faithful—if cold—to his wife, and indulges only his grandson.
But things look different when the light fades and evening begins.
She smiles because she's too tired to cry. She engages with her guests because if she didn't, she'd go mad from loneliness, and if she didn't raise her son to be a little gentleman, her husband would "remedy" the problem with some distant boarding school. She couldn't bear to be parted from Scorpius, who is the only one who elicits a smile from her these days.
He is faithful and cold to his wife because the one time he strayed, he fell in love. Now, the woman he loves is unattainable. He indulges his grandson because he has a guilty suspicion that those blue-grey eyes are bluer than they are grey—like his, not like Draco's. He knows it may not ever be enough, but it's something to be there for the boy who might be his son.
When the light is gone entirely, they drink to block out the memories of their affair. It feels like a lifetime ago. She had been a beautiful young woman, unpracticed in the ways of the world. He had been in his prime. She never cared for her husband; he had fallen out of love with his wife somewhere between the second war and Draco's engagement. He was the Byronic anti-hero of all the storybooks she'd ever read; she was the first damsel in distress he had ever had power to save. They came together in a moment of weakness and realized with horror as the morning light crept in that there was something more there than wish-fulfillment. Affection in a dispassionate world. Love where love was not supposed to be. There is nothing more frightening than knowing that except for this one, forbidden thing, the rest of your life is waste. No matter what else they forget in drunken solitude, they know that their love has been wasted.
In the morning, the hangover hits. Draco and Narcissa pretend not to notice. Maybe they don't. The headache fades, but by afternoon, his promises still ring in her ears and she cannot hide her wistful glances at nothing and her perfume still tickles his nose and he cannot hide the nostalgic smile. But they put on their bravest faces because Astoria and Lucius both know that a crack in the smile is better than a broken home.
Disclaimer: All recognizable characters belong to JK Rowling. "Perfume and Promises" is a song by Idina Menzel.