Harry returned to Grimmauld Place brokenhearted. Sirius Black was dead and his murderer had escaped. He collapsed onto his bed numb. He'd failed to save his godfather. The tears came now, he couldn't stop them. Finally he fell into a painful sleep.
Harry smelled jasmine, it began to rouse him into wakefulness. He slowly opened his eyes and found two things were different than when he'd went to sleep that night. The first was that Bellatrix LeStrange was atop him on the bed, her hands resting on either side of his head, she was staring at him with a little smile on his face. The other thing he'd noticed was that he had been tied to the bed with thick cords, he couldn't move his arms or his legs.
"Good morning little Potter..." She said as the smile grew "Yes, you are at my mercy at the moment. However, I am only restraining you so that you will listen to me. Firstly, I did not mean to kill my cousin..he was dear to me. Secondly, the Dark Lord has decided that my life is more expendable than I would like. I was directed to not come back until I had found and killed you. I've heard enough about your history to know what happens to Death Eaters who come against you, I am insane but not stupid."
Here she raised her wand and removed the silencing charm that Harry hadn't known she'd placed on him and continued. "I Bellatrix LeStrange, do swear on my magic that I will cause no harm to Harry Potter, and that I hereby forsake my former master Lord Voldemorte. So mote it be." A spark from her wand signified that it was a real magical oath.
Harry looked to her confused. "So, what do you want from me?" He asked her, wanting to sound defiant, but for some reason his voice was soft.
She looked down at him, her hair was softly touching his face, it tickled slightly, but Harry was still too confused to laugh at the feeling. "Well, first thing is it's not what I want Harry, it's what I can offer you. If you provide me with asylum here, I will teach you the tactics of the Death Eaters and tell you what I can of Voldemort's plans so far."
"But, how can I hide you? The Order comes here constantly..." Harry began but was muffled as Bellatrix smirked and pressed a finger to his lips. "I have a glamour I plan to cast. To all the world, I will appear as someone else. I know that chewed up Auror can see through my disguise, so I will avoid being around him. Grimmauld Place knows how to protect a Black, I can keep hidden from him. Again, Harry, I am not stupid. I may have joined a group dedicated to the destruction of everything you hold dear, but it was not because of lack of foresight. The next thing we will do is take me to Gringotts. You are Lord Black and Lord Potter, you will annul my marriage to that witless oaf Rodolphus and thus I will be Bellatrix Black once more."
She was smiling again and sat up, sitting on Harry's lap. "You are free to refuse me Potter, but I can promise you this; if I leave this place, you will never know how to protect yourself from the Dark Lord."
Harry sighed softly and looked to his bound wrists and ankles. "Alright, for now I'll trust you, can you kindly remove these bindings so I can get up?" He said motioning with his head, Bellatrix grinned and stood up, casting the counter spell and freeing Harry. "Handle your daily needs, when you return to this room, I'll be in my new shape. We can go to Gringotts after breakfast."