Narcissa lies awake, her heartbeat quick and palpable no matter how slowly she tries to make herself breathe. She is curled up on the left side of her bed, though there is plenty of space. The other side is cold and vacant, as it has been since Lucius was taken from her, now safely incarcerated. Draco, too, is gone — her heart jabs harder at her — whisked away by the gaudy-red Hogwarts train as though this is just another ordinary year.
The presence of the Vow is like a knot at the base of her skull, tightly grasping one end of a magical rope drawn taut between Severus and herself. At first it was uncomfortable, and she found her hand going time and again to the nape of her neck, rubbing irritatedly at nothing. But now, with her house dark, cavernous, and still as a tomb, it has begun to feel curiously comforting.
Not for the first time, she goes over that night in her mind. She hadn't planned to do what she did, nor did Severus ask for it. But when Bella had gone, and she and Severus were alone, Narcissa realised that she could not walk away in his debt. She knew, too, that she had nothing left to offer but herself.
She remembers lying naked before him, her face still stiff with tears, getting gooseflesh and pebbled nipples in the midnight cold. He did not undress. Instead he pulled his prick out from his robes, looking at down at her with eyes as dark and remote as the sky. She reached out for his arm — a moment of weakness — and he flinched. Her fingers closed, and she drew her hand away.
When all her body was his to enjoy, she was surprised at what he wanted; vividly she remembers the hardness of his grease-coated fingers between her cheeks. She hadn't been taken that way since she was a young woman, and when he first entered her, kneeling between her thighs and lifting her hips in cold hands, she let out a small sound of pain. He didn't stop, but he slowed and met her eyes. She felt as though he was gauging her response as he moved in her, despite his stony look — being careful of her while pretending he was not.
It had been so long since Lucius had gone, and as her body recalled the art of taking a man's cock this way, her bare and untouched sex began to throb with desire, trickling wetness down onto the place where the two of them joined. Forbidden from holding him, she instead wound her hands tightly into Severus's bedsheets, struggling to make no sound that might be overheard.
Severus neither moaned nor spoke — nothing so vulnerable as that — but his breath grew faster and harsher as they moved together, and she found herself fascinated by that little revelation of his humanity, of mortal flesh and blood. She pushed back against his thrusts, now savouring the stretch and ache, that strange roundabout pleasure she'd almost forgotten, filtered through pain and pulling at her from within. The bedsprings creaked beneath their rhythm, and outside, a barking dog echoed faintly in the dingy Muggle street. When Severus spilled himself inside her, his eyes squeezed shut, and as she pressed herself against his trembling hips, she had the queer idea that it was the only time she'd ever seen him not looking.
Narcissa remembers this, blankets drawn tightly round herself in her own bed. She warms her hand between her thighs, fingers playing softly in the wetness that comes with the memory. She doesn't try to make herself come, as she knows that moment of animal joy would only be followed by redoubled loneliness.
Again, she turns her mind to the feeling of the Vow's knot at the back of her neck, sure and true. Proof that Severus is bound to her. That Draco is safe.
She doesn't allow herself to consider a time to come when the knot might loosen not because the Vow has been satisfied, but because the breath of the man at the other end of the rope has at last been stilled.