a/n I
Betalove to viv-heart, without her you this chapter would be quite German :D
Also, sorry for the delay, explanation at the end!

The Black library on the first floor of 12 Grimmauld Place wasn't as huge as one would think it would be in an ancestral home. And yet it still had thirteen books about ancient magical laws. Five were from the tenth century when wizardkind became more organised. Those were hefty tomes bound in black leather with texts written in Latin with a tiny script. Six books were from the time of the International Statue of Wizarding Secrecy and were much smaller, with an easily readable script and in English. The last two books were from the early twentieth century and looked much more like a legal text than the others.
Hermione decided to start with the oldest books as they were closest to the instalment of laws she was researching and therefore probably the most accurate.

The next time she looked up Harry stood in front of her and the room was quite a lot darker than before.
"Are you alright 'Mione? You read the whole day and haven't eaten a bite since breakfast," he asked a tad worried and she blinked owlishly at him and before turning to look at the clock on the other side of the room. It was indeed 7 o'clock in the evening.
Hermione stretched her legs and noticed the pain caused by her lack of movement for the last hours. She carefully closed the old book having reached the last page and put it aside to the two others she had read over the course of the day. Only one had a piece of parchment as a bookmark in it.
"Why didn't you call me down for lunch?" she asked with a yawn.
Harry shuffled his feet awkwardly. "We did call you and after the second time you cast a Muffliato and a locking charm we weren't able to get through. We only tried it now because dinner is ready. Kreacher has really outdone himself."
Hermione blushed. She didn't remember anything from the interaction and she didn't like not having full control of her senses. Ever since her third year and the disaster with the time-turner she tried to stay aware when studying. She had occasionally lost time while doing all her homework and revision and it had scared her quite a lot at that time.
Harry offered her his hand to help her up and steady her when she swayed a little at first. They walked down to dinner and Hermione had to admit that it was a right feast Kreacher had cooked. The ancient elf bowed politely when they entered and Hermione smiled at him.
"Kreacher is happy to present the dinner to the conquerors of the vile Dark Lord who killed his Master Regulus. Kreacher hopes everything is to the taste of the Masters and Mistress," he exclaimed with a bow to the table where Ron was already seated.
Hermione sat down on the opposite side of Ron while Harry took the place on the head of the table.
"What were you reading all day, 'Mione?" Ron asked around a mouthful and Hermione tried not to scold him for it, again.
"Law texts. I have a feeling that the Ministry isn't too happy that I saved Malfoy," Hermione frowned. "I want to be prepared to defend my decision. After all it is backed up by laws quite to the contrary of their actions. Harry, will you come as well and tell them how he refused to tell Bella who we were? And how Mrs. Malfoy lied to the Dark Lord about you?"
He nodded and they all resumed eating. When they were on the run they had learned to eat first and talk later. You could never know how much time you had left before Snatchers would turn up.

After dinner they retired to their rooms, too sleepy to be social. But even though Hermione was extremely tired, her brain didn't find any rest.
She couldn't stop thinking about what she had found earlier that day. The law texts she had read were Latin but thanks to her ambition to be able to understand every spell they were taught she had learned the supposedly dead language to the extent to being able to read it just like English. Still she would need to translate the text for the trial. While mulling over the best translation for "per alium" she finally fell asleep.

Narcissa couldn't sleep. Hermione had written her, that she was searching for ancient laws and the blonde wondered where. If she searched the tomes in Hogwarts she wouldn't find much. Life debts were considered darkest magic since the 50's and were therefore no longer present in the school library. On the other hand she had found and destroyed all of the Dark Lord's horcruxes with the two boys and those were really despicable pieces of magic. If what Draco had told her about the girl was true, she researched everything quite thoroughly before taking action. Her son had ranted about it in third year and Narcissa prided herself to never forget any information about people.
Where could she have gotten books about them? Yaxley had told the Dark Lord last September that the trio had stayed at the old Black townhouse for a while. Maybe they returned there after the war? If that was the case, Hermione would have the second darkest library of wizarding Britain at her disposal and would definitely find those laws.
Narcissa surely hoped that to be true as her son's life depended on these laws and their legality. If the Wizengamot decided that these laws were outdated and not longer legally binding, they could decide to execute him on spot. The Malfoy matriarch wasn't going to let that happen.
So she closed her eyes and descended in her mind palace. It was a occlumency practice she had learned as a small girl and had come in handy when the Dark Lord, no Voldemort, had returned. Now she went to the huge library which occupied most of the space in the palace. She opened the huge oak double door which had intricate inlays of pearl and rubies and lead to a two floor library. The library had shelves along the walls and a network of dark and light aisles in the rest of the room. Here and there stood a few tables and reading armchairs - some lit with candles, some reached by the light from the glass dome above.
Narcissa mentally went along the light aisles searching for those old law books. She kept the dark magic in the light and the light magic in the dark to always remember both sides. Finally she found the section she had looked for. "Leges antiquae" was written on the headboard in gold letters. She let her fingers travel over the spines of the books and concentrated on the laws about life debts. One book leapt to her hand when she touched it and she opened it.
It was an ancient tome, bound in black leather and hand written in Latin in a tiny script. Its title was "De legis vitae et potentiae magae" and a year was written on the bottom of the title page, 934 A.D., sixty years before Hogwarts was founded. Narcissa browsed the pages and found the law. She smiled to herself and retreated from her mind palace.

When she reopened her eyes Lucius looked at her curiously.
"What did you search for, dear? You seemed to be deep in thought," he asked quietly to not raise any suspicion from the guards. They were lucky to be in one big cell in the Ministry instead of small cells in Azkaban, but they didn't know how long their luck would hold on if they were caught whispering too often.
Narcissa sighed. "I searched for a book Hermione would need to convince the Wizengamot to let Draco live."
"Did you find it?"
She nodded. "Hopefully it is still in the Black library. Maybe Hermione has found it as well. I will write to her and ask."
Lucius leant back. He didn't look like the man he had been just two years ago. His cheeks were hollow, he had dark circles under his eyes and his much thinner hair looked more grey than platinum. He was broken. His stint in Azkaban, the continued presence of the Dark-, no, Voldemort in their house and the danger he and his family had been in for the last year have taken their toll. He looked much older than his fourty-five years and Narcissa dreaded to look in the mirror because she knew that she probably didn't look much better.
Her gaze fell on her son, lying on one of the two beds in their cell, who had even in his sleep a deep frown on his face and had aged prematurely as well. She sighed deeply and sat down next to him to caress his head like she used to do when he was younger. The happiness she had felt in the moment he entered the Great Hall had been overwhelming. She had been so sure that she had lost him after having found him again just hours earlier. He brought out the best in her and she was fiercely protective of him and his father. If Hermione hadn't been…
No! Narcissa chastised herself. She wouldn't let her thoughts wander in that direction. Hermione saved him and there was no "what, if" anymore.
After a last caress over the wrinkled forehead of her sleeping son she stood up again and started to write a letter to the young witch who saved her from so much grief. She refrained from expressing her gratitude again but settled on a much friendlier tone than she normally used in her correspondence. She was going to give the letter to the guard in the morning.
For now she lay down next to her husband of twenty-one years and he pulled her in an embrace. She wondered fleetingly when they had been that affectionate the last time before she drifted of to sleep.

When Hermione walked down for breakfast the next morning both boys were already sitting at the table, eating. Kreacher asked whether she would prefer coffee or tea and scurried of to bring her a plate and her mail. She got only one letter, which had the stomp of the Ministry checked letters, indicating that it was probably from Narcissa. The still tired witch read it while drinking her first cup of tea and was pleasantly surprised by the contents.

Dear Hermione,

my son always told me how much time you used to spent in the library and I therefore have concluded (hopefully correctly) that you love to research and learn from books. Your successful hunt for Horcruxes tells me furthermore, that you also were able to get your hands on books about very dark magic.
It might surprise you, or maybe not at all, but since the fifties life debts are seen as darkest magic, for they can be used to force people into slavery or to do things they would never do in their own free will.
I am sure you already started searching for books on the laws of life debt, but I wanted to recommend one to you never the less. It is called "De legis vitae et potentiae magae". I read it during my youth in the Black townhouse and I remember it to be quite informative on the subject. I hope you are fluent in Latin or very good with the translation charm as it is written only in Latin and I don't remember any translated copies.
I hope I was able to help you.
Kind regards

Narcissa Malfoy

Hermione smiled. She had indeed already read the book Narcissa suggested, but she was really happy, that the older witch had been so thoughtful to recommend it.
Suddenly the letter was snatched from her hands by Ron and both he and Harry read it in silence. Ron seemed to grow angrier with every word but Harry smiled a little bit, seemingly coming to the same conclusion as Hermione had.
"Unbelievable how that woman tries to gain your trust! I am sure she just wants you to speak in her favour at the trials so she doesn't have to go to Azkaban!" Ron spat as he had finished the letter.
Hermione looked at him incredulously. "Are you serious, Ronald? How should suggesting a book on supposedly darkest magic help her staying out of Azkaban? This recommendation itself could give her trouble because she was born after the law was issued and therefore shouldn't have read it at all! But not only does she write it in a letter which will be checked by the ministry, she also hints were the book could be." During her speech Ron sank back into his chair and Harry looked majorly uncomfortable. He tried to diffuse the tension in the air by putting a hand on the shoulder of his two best friends but they ignored it and just glared at each other.
"Please, 'Mione, calm down. You as well Ron. I don't think that Narcissa is so dumb that she would try to manipulate Hermione into helping her. She stated from the beginning, that she was interested in Hermione's friendship and I think this letter is just that - a friendly gesture," Harry argued and Hermione nodded along. Ron still seemed furious and left the kitchen, going upstairs. The two best friends exchanged an equally annoyed and worried look and sat down to finish their breakfast in silence.
Just as Kreacher had vanished the rest of the meal Ron came back down and looked at Hermione apologetically.
"I am sorry, 'Mione. I overreacted. I guess I am so used to the Malfoys being the bad guys that I can't see them as, well, good guys without ambiguous thoughts," he said looking down at his feet.
Hermione smiled and pulled him into a brief hug. "That's alright. I don't trust them completely as well. It is just so new that I have difficulties to believe it, but Narcissa has been nothing if not genuine to me so far. I am inclined to really give her and, if they prove themselves, her family a second chance."
Ron grumbled a bit but smiled in the end. "I'll try to trust your judgement, 'Mione. You are after all the brightest of us."

a/n II
I hope you liked it! Real life didn't like me for the last two weeks and my muse was sulking in a corner of my head and refused to come out. But now the spring finally has come to Germany and she is extremely happy so weekly updates should be in order *looks sternly at her muse*. This mind palace is inspired by the mind palace of Sherlock, but it is a common method to organise ones mind.

For translation (I used frag Caesar):
"Leges antiquae" - "ancient laws"
"De legis vitae et potentiae magae" - "Of laws of life and magical power"