After Bellatrix Lestrange acts as a bonder to the Unbreakable Vow made by Severus to Narcissa at his Spinner's End residence, they start to take his leave and go back to Malfoy Manor.
However, Snape says, "You may leave, Bella. Narcissa, may I have a word with you in private".
"Its okay, Bella. Go ahead, I'll join you later" said Narcissa without realizing what a terrible mistake this was going to be. But there was no reason to suspect Snape. He was her family friend. He was the favorite teacher of Draco, and now he was going to protect her son. However, Cissy didn't realize the price she was soon going to pay to this wretched wizard for that.
Perhaps, a background of Snape's predatory sexual behavior is important here. Of course, Dumbledore would have you believe that Snape was all saint since he was pretty loyal to the Order. Maybe he was, but he was also an expert in occlumency, and Dumbledore wasn't granted access to this secretive and lustful part of his mind that always used to crave a woman's body desperately.
Snape had had physical sex with several women till date. The females who resisted him, were his special favorite. Though he could have easily put them under the imperius curse, or subject them to the love potion, it gave him utmost satisfaction to actually rape his targets whilst he enjoyed their wails and screams with a pleasurable delight.
Perhaps, this deranged mentality of Snape was caused by his loser complex. Since he had lost Lily, the loser had over the years found himself desperately looking for sexual gratification in exploiting the physical bodies of his innocent victims.
After Bella was gone, Snape locked his door behind her. Then he turned around and walked towards Cissy.
"Yes. What is it that you want to tell me Severus" asked Cissy.
"I want you to promise me one thing Narcissa" Snape replied holding out his hand.
"What promise" replied Cissy placing her hand over his.
Now that they were absolutely alone, and his target was totally within his power, the womanizer started making his moves. He knelt before Cissy still clasping her hand and kissed it deeply.
Snape had a profound sense of smell through his abnormally large hooked nose. Snape liked to smell the body odour of his female target before starting his invasion. The blissful aroma emanating out of Narcissa's pale white hand now confirmed its owner's helplessness and desperation for her son.
"That you will not stop me from doing this" breathed Snape, and in one swift movement, he stood and locked his arms around Narcissa's waist and pulled her body towards him. His body was pressed against Cissy's and his face was hardly an inch away from hers.
"What are you doing Severus" asked Cissy, nervousness filled in her voice?
"Exploiting you sweetheart, what else" replied Snape.
"No" screamed Narcissa loudly, pulling herself away from the womanizer. "No, No Severus. I belong to Lucius. My heart, soul and body all belong to him".
"Let it be" said Snape coldly. "I'm just borrowing them for a while".
"You cannot Severus, I consider you as my best friend. How could you do this".
Snape looked at Cissy, his cold and calculated eyes boring into hers. "Now look Cissy" said Snape calmly, "You want my help in securing Draco's life and health at Hogwarts, right? Consider this as my price".
"You can't do this Severus, you have made an Unbreakable Vow".
"Have I now, Narcissa? And do you really think this kiddy magic of yours could not be undone by a shrewd and cunning wizard like Severus Snape".
"Also, what If I told the Dark Lord about your treachery, Cissy. About how you roam around trying to secure your son's future disobeying the Dark Lord himself".
"I trusted you Snape, and you are blackmailing me" said Cissy in a weak voice filled with despair and helplessness.
"Oh, really Cissy, am I now? Is asking for a fair share termed blackmail in your books?"
"I am just trying to help you darling" said Snape wrapping his arm across Narcissa's behind.
Although it was a torture to feel the filthy hands of this wretched creature touching her body, Narcissa forced herself to remember what she had herself said to Bellatrix a few hours earlier:
"There is nothing I wouldn't do anymore".
So, Narcissa decided to let herself played by this womanizer now. She could do anything for Draco, after all. Hopefully, this will be over soon.
Severus then proceeded to take out her robes and started pulling her skirt from behind.
"Noooooooooo Severus. Its improper." screamed Cissy.
"Shhhhh. Wail all you want Cissy, no one will hear you here".
Now Cissy was left only in her black colored bra and panty, tightly crossing her arms trying to shield her breasts from this monster of a wizard.
The main problem with Snape was this insatiable lust lurking somewhere in the deepest corners of his brain that was activated only in front of a sensual form like the one presently lying before him.
Snape removed his own robes, then lifted the beautiful Cissy into his manly arms.
Narcissa felt a sense of powerlessness take over her pale white body as she felt Snape's arms lift her and place her over his threadbare sofa. Snape then proceeded to press his body upon hers, wrapping his both arms across Cissy's backside and locking her into a tight embrace.
"Aaaaaaaaarrrrrrrrrrgggggggghhhhhhh" wailed Cissy like a cat in distress. Narcissa had just felt the sensations of extreme pain and extreme pleasure at the same time.
Snape was now directly upon Mrs. Malfoy. His chest pinning down her firm and expanded breasts, his abdomen and hips pressing hers into captivity. He could smell her sensual body aroma now.
And then Snape's black eyes fell into her blue ones and they were suddenly full of lust. Snape then started kissing her red lips passionately. They were soft, plump and juicy and emanated a sensual nectar which mesmerized Snape's all senses.
Once Snape was done with her lips, he placed his teeth in Cissy's black bra and gently pulled it down.
Now that she had endured this much, Narcissa started feeling this wasn't as bad as she had expected. Hell, she had almost started liking it.
Snape then started biting Cissy's right nipple.
"Aaaaaaarrrrrrrggggghhhhh. No Severus, No. You are defiling me".
But Severus was too busy enjoying her bodily aroma and her electric touch to actually listen to what she was saying.
The scent and odour emanating from Cissy's sweat and body was now too much for the Hogwarts Professor to bear. His eight inch cock had by now become a rock, and the only destination it knew was Narcissa's vagina.
Snape lowered her panty just enough so that he can insert his cock inside her sublime vagina. The thing that just came inside Narcissa was giving her immense pleasure now. She suddenly wished for Lucius to never come back from the prison. Things won't be that bad for her after all!
Snape and Narcissa were totally inside each other now, both desperately wanting this to go on and on till the end of time.
However, change is the only constant in the wizarding world. Dark Lords will come and go, and so will great witches and wizards. But at that instant, being blissful in each other's embrace, these two friends became a lot more intimate from that day. What began as Narcissa's rape, in fact, ended up in she discovering an intimate ally and confidant with whom she could not only share her deepest secrets, but pleasures and excitements too!