It is an enchanted place where Snape and Narcissa meet.
It is refreshingly different to the places frequented by the Death Eaters. It is a Muggle apartment with large windows. The bedroom is drenched with sunlight. He thinks that possibly that is a far greater comfort to them both than each other.
It is, he suspects, the most enchanted Muggle home in the world, with the possible exception of the home of Hermione Granger's parents in Australia (a fact which Hermione would be horrified to know he knew). It is a place of safety. Not for long, but for moments in time.
Their excursions there are frequent. Bellatrix assists them. She approves of their affair. Snape thinks with revulsion that he has gone up in her estimation since killing Dumbledore, and Lucius has had a marked drop in popularity. Bella believes that Narcissa is simply playing the game. She believes that because she has no comprehension of the more human motives that draw people together.
Which is not to say that he and Narcissa have a deep love bond. They don't, and there is no pretense of it on either side. But Narcissa is lonely - deeply lonely. Terrified for her son. Lucius, never the most attentive husband, is now a frightened and sterile figure with nothing to give her.
As for Snape, as far as he has allowed Narcissa to believe, he is recovering from a betrayal by an unnamed lover, an estranged member of a Pureblood family who showed initial sympathy for the cause, but then turned blood traitor of the worst kind. He believes he has dropped enough hints to give the impression that his lover was her erstwhile niece, Nymphadora Lupin.
The reality is that he is lonely, too. Dumbledore was a rather poisonous father figure, on the whole, but he and Hogwart's were all that Snape had left. Not that he ever believed he was greatly loved at Hogwart's, but it was a family of sorts, and a home.
And now they are gone.
So now there is Narcissa. Voldemort encouraged the union. Snape thinks he intends to kill Lucius in the fullness of time, and that he likes the idea of Narcissa having another man on her arm. Voldemort has a deep distrust of women on their own, distrusts women in general, actually. They are too difficult to understand and predict, too prone to such inconvenient traits as compassion and inspiration (always excluding their resident sociopath, Bellatrix). In fact, the only person who doesn't know and approve of the affair is Lucius. Or perhaps he knows but doesn't care. Either way, they are free to come and go from the apartment at will.
Narcissa arrives as he is thinking these things, and he begins to unbutton his collar, automatically, without looking at her. But instead of removing her clothes without ceremony as normal, Narcissa hesitates, and that makes Snape hesitate, too.
"I think we should stop doing this, Severus," she says. Nervously. Biting her lip. As though she has been planning this but her conviction has left her.
He is a little surprised, but he knew she would end it one day. Whatever else has happened, she loves Lucius. Perhaps she has finally perceived the fate Voldemort has in mind for him.
He carefully re-fastens his collar. "Very well."
"It isn't - it isn't that I don't want to -"
He holds up a hand. "Really, Narcissa, you needn't explain yourself. I will respect your wishes." He turns away and picks up his cloak, feeling a twinge of disappointment. It doesn't matter, not really, but the comfort of flesh against flesh has helped. Just a little.
"You call me Lily," she blurts out.
It is with great effort that Snape does not react. In a smooth movement, he puts his cloak back on the chair and turns to face her again. "I beg your pardon?" he says with an air of mild curiosity.
"Lily," she says again. Then, in a rush, "Sex is a powerful thing, Severus. I fear that this is breaking down defences in you that should not be broken down."
He understands that she knows these things, not as a witch, but as a woman. Against this, Occulumency can do little.
What now? he wonders. He is in grave danger. But she surprises him.
"You saved my son," she says. "You kept the Unbreakable Vow. I am in your debt, Severus."
"I did not do it for reward," he says in a low voice.
"No," Narcissa agrees. "But it is true anyway." She meets his gaze fully. He realises with a jolt how rarely she does that. "You feel responsible for Lily's son, Severus."
"Preposterous!" he sputters. "That's tantamount to accusing me of-"
"I accuse you of nothing, Severus. I tell you only this: that you have saved my son, and if yours crosses my path, I will do what I can for him."
"Potter is not my son," he says through gritted teeth.
"But you wish he was. You don't like him, sometimes you even hate him, but how you wish-"
He grabs her by the arms then. She lets him do it. Watches him patiently. Eyes grave. He feels things welling up in him - things too dangerous to risk spilling out - and so he kisses her, hard, passion and pain flooding out of him. And maybe just a touch of hatred - hating that she knows him like this.
She returns the kiss, wrenching her arms free and wrapping them around his shoulders. She understands, he knows she does, and he hates it with his entire being, but he is powerless to stop reaching out to her. Understanding - the thing he craves and loathes. Craving it made him love Lily. Loathing it made him lose her.
"I'm a Metamorphagus," Narcissa whispers. He remembers that she shares Nymphadora's bloodline. "No one knows but you. I could-"
He understands at once what she is offering - who she is offering to be for him - but he cannot allow it. For a thousand reasons.
Touching her face, he says with a voice that is unusually gentle, "That would be...unwise."
She nods, her head bowed until he finds her lips again.
Their lovemaking is vibrant, but gentler than usual. He buries his head in her hair, closes his eyes as he roams her body. Immerses himself in a way that he does not normally dare. Sometimes she is Lily, sometimes Narcissa. She does not speak, but lets him do as he likes with a faraway look in her eyes. He wonders if she is thinking of Lucius - the Lucius she married. He does not begrudge her if she is.
It is the closest he has come to true union with anyone in his life.
At last, it ends. They look at each other, resting side by side.
"You were right," he tells her, stroking back her hair from her face. "It does need to end."
"I haven't forgotten my promise," she says, taking his hand. "I consider it as unbreakable as the vow you made me."
He wants to tell her to forget it. That she has the whole thing entirely wrong. But he knows that Potter may have need of her promise one day, and he knows that she knows him. Rather better than he would like.
"All right," he says.
He closes his eyes, and she leans in and kisses him for the final time.