This is totally AU. I don't own Harry Potter, this is just my own spin on what happens after Harry & co are captured by snatchers. Ron is gone and replaced with my own character.
Background:
Right after they are captured by Snatchers and spend time at Malfoy Manor, Dobby rescues everyone and takes them to Shell Cottage. When he comes back for Hermione, Harry and Addie, he is hit by Belllatrix's knife and he accidentally takes them to the Marauders 7th year during the Easter feast. Harry and Addie are a couple.
With a 'pop' they arrive in the Great Hall. Hermione collapses and Addie -dripping blood from gashes on her stomach and the 'blood traitor' carved into her arm- tends to her while Harry, with his rapidly deflating face falls to his knees with Dobby and the Hall falls into silence as they watch the elf give his last words to the beaten and bloody trio. After Dobby takes his last breath there is a ringing silence that is not broken until Addie whimpers in pain and shock as she stares at the rapidly growing puddle of blood at her feet.
All eyes in the Hall are drawn to her as she drags herself to her feet and limps to Harry. Placing her hand on his shoulder, she kisses his temple and gently lowers Dobby's eyelids.
"There. Now he could be sleeping." (A/N: spoken by Luna, HPDH) Then she raised her eyes and scanned the great hall, locking onto the greasy haired boy whose face was frozen in horror and recognition as he stared at her steadily bleeding wounds.
"Severus." Everyone's eyes flashed to him as whispers broke out. "Help me." She took a feeble step towards him, then her eyes rolled back in her head and she fell to the ground.
At this point there was a complete uproar that was only silenced by Dumbledore's loud shout.
"SILENCE. EVERYONE STAY IN YOUR SEATS." He rushed down the steps with Madame Pomfrey and Professor McGonagall right behind him. Severus had leapt to his feet and to the shock of nearly everyone he all but sprinted to the fallen girl. Gently he rolled her to her back and with Harry's help he lifted her shirt, exposing the wounds and started murmuring incomprehensible words.
The Marauders realized at this point that all three newcomers were wearing hoods that covered most of their faces and they suspiciously rose to their feet. Dumbledore seemed to realize this as well because as he determined that both Harry and Hermione were stable he casually pointed his wand at Harry and asked calmly, "Who are you?"
The Hall was silent, though most of the Gryffindor table had drawn their ands. Everyone waited with baited breath for the answer but before Harry could even open his mouth, there was a quiet groan from Addie. Everyone watched as she slowly stirred and Snape sat back, satisfied with his work. He peered at the face under the hood and saw dark grey eyes under the hood. To his shock, she sat up and as jaws dropped around the hall she leaned forward and kissed his cheek before audibly saying,
"I owe you a life debt Severus Snape."
She slowly rose to her feet and walked to Dumbledore, stepping in front of Harry and pushing his wand away. She then turned to Harry and silently conversed with him. Finally she nodded and turned back to the Headmaster,
"This may come as a bit of a shock to you." She slowly removed her jacket, lowering her hood last. As the residents of the Great Hall caught a glimpse of her face they gasped, and eyes flicked to Sirius and Regulus Black, because with her grey eyes and black wavy hair she could have been twins with either of them. She smirked slightly when she saw their reactions, "My name is Addison Black."
Before chaos could break out, Harry lowered his own hood. There more gasps and James Potter had to sit down before his knees gave out.
"My name is Harry Potter." He glanced at the Hermione's unconscious figure and pushed her hood back as well. "This is Hermione Granger." He looked at Dumbledore and smiled slightly, "We are not Death Eaters."
There was a collective sigh of relief, and Addie let out a bark like laugh. She stretched languidly, revealing six inches of tanned skin, fresh with scars and still smeared with blood. She ran a hand through her hair and glanced around. Her eyes fell on Dobby and her face grew stony. With a wave of her hand she levitated the elf and turned to Dumbledore, who looked mildly surprised.
"You can perform wandless magic?"
Addie snorted. "I'd be dead otherwise."
As the morbidity of that statement sunk in, Madame Pomfrey cleared her throat, "This young lady needs the Hospital Wing."
Addie glanced at Harry and jerked her head, "Go on. She's gonna need you, and I've got this." Harry kissed her on the top of the head and jogged after Hermione.
Addie watched him go and then turned back to Dumbledore. She gathered Dobby's bloody body into her arms and blinked back tears.
"May I bury him on the grounds Sir? He loved it here."
If that statement confused Dumbledore he didn't show it, he merely inclined his head, "Ah yes. Of course. Would you like me to accompany you?"
She looked at him, "Only if you wish." She turned and began walking away but had only taken a few steps when she changed her course and came to a stop in front of Sirius. He cautiously stood up and looked down at her. Addie gazed up at him with a faint smile on her face,
"This may sound crazy but can I please have a pair of socks?"
Sirius blinked. Her appearance was startling; her grey eyes were exactly like his own, as was her facial structure. Even her wavy black locks were like his. His masked his shock though and nodded, flicking his wand to summon a pair of socks. He caught them as they soared towards him but when she reached for them he shook his head, "I'll join you."
Addie smiled up at him, "Thank you." She turned and began walking again with Sirius close at her heels. Without a moment's hesitation James, Remus and Peter followed as well.
Addie walked steadily towards the doors but then swerved at the last minute and let her feet take her to the Slytherin table. There was a bit of mumbling at this but she ignored it as she stopped in front of Regulus. He looked up at her and he too, was shocked by her appearance.
She smiled at him sadly, "May I please have a Galleon, a Sickle and a Knut?"
He nodded and dug in his pocket for the coins. He dropped them into her outstretched hand and she smiled again, "Thank you."
Once more she turned and walked towards the doors, not looking back and not stopping. At the Entrance Hall she found Harry waiting for her, it was only then that she turned and surveyed those who had followed her. Sirius, Remus and James headed the group with McGonagall and Dumbledore right behind them. Next came Lily, Marlene McKinnon and Alice Prewett. Then behind them came nearly all of Grffindor, Hufflepuff, Ravenclaw and even a few Slytherins. She noted with slight hatred that Peter had disappeared into the crowd.
Harry pushed a few locks out of her face, "C'mon baby."
Addie squared her shoulders and marched down to the lake, stopping when she reached the large willow on the far side. She looked to Harry who flicked his wand. She then laid her jacket to line the hole that had appeared in the ground. She knelt and placed Dobby gently on the jacket. Turning to Sirius, she took the socks he held in his outstretched hand and everyone watched curiously as she tugged them over the elf's tiny feet.
Harry wiped his eyes and walked over to the forest, grabbing some stray branches, which he transformed into a small cross. He placed it at the head of the grave as Addie wrapped Dobby's little fists around the three coins. For the last touch, Harry shrugged out of his own jacket –revealing badly scarred arms and shoulders- and laid it gently on top of Dobby. With a wave of Addie's hand and a flick of Harry's wand the dirt filled in on top of the elf and 6 words appeared on the cross. Stepping back, Addie began to speak capturing everyone's attention; even the Forbidden Forest seemed to fall silent.
"Thank you Dobby for saving my life. For getting me safely out of danger. I owe you everything and I'm sorry this is all I could give you. I will forever wear my scars as a badge of honor for you. It is because of you that Voldemort does not have us in his clutches. It is because of you that the diary is gone and the Basilisk is dead. It is because of you that Harry survived the hour in the Black Lake. It is because of you, my sweet little elf, that we are alive and sane. And so I swear to you Dobby, I will find her. I will find her and I will avenge your death. I will take her life like she took yours. Sleep well my dear." At this her voice cracked and with one last wave of her hand she conjured a beautiful orange flower and placed it on his grave.
Then she took Harry's outstretched hand and the mysterious pair parted the crowd as they walked slowly back to the castle. The large crowd surged forward and group-by-group wands were waved, and though they did not know the tiny creature, the students of Hogwarts placed flowers on Dobby's grave. As they passed they all looked at the little cross, and with much confusion read the six words.
"Here lies Dobby. A free elf."