Lily learns to knit in her seventh year, as an activity her grandmother suggests for when she's stressed. She knits when she's scared about the war, or angry that the adults aren't doing enough, or confused about Potter's personality change over summer, or when she knows that Marls and Dorcas are heading for what she hopes will be the final blowout before they realise they're in love.
(For some reason Lily can see it in everyone but herself).
Lily starts the year asking for yarn every month, but by Christmas her parents are sending her yarn every other week at least. She knits scarves and mittens and hats, and Remus will die before he admits that he kept every single one of the sweaters she gave him that winter, when the warmth the wolf brought with it abandoned him every New Moon leaving him wracked with shivers, and she plied him with hand knit clothes and warm tea.
(In the privacy of his own mind he hopes he's not imagining the faint smell of parchment, strawberries, and something else that could only be described as purely Lily.)
One day Lily loses a knitting needle, and, anxious about the war, and her parents, and Petunia, thinks nothing of using her wand as a replacement until she comes out of her haze and sees she's knit an entire sweater in about an hour and a half. Even though she had been using only a single color of yarn, the sweater was practically dancing with all the odd color changes. When Lily tries it on, she notices runes knit into the inside of the sweater. Runes like Protection, Love, Hope, Family. When the sweater settles around her Lily stops breathing, feeling her father's strong arms, her mother's hand on her back, and Petunia wrapped around her like they hadn't been since before magic.
(Lily cries.) (When Sirius comes downstairs to sit in front of the fireplace, he finds a crying Lily Evans wearing an odd, multi-colored sweater.)(He sits beside her, stares at the flames, wraps an arm around her quaking shoulders, and uses the cover of her sobs to let out a few tears of grief for the brother he loved but could only watch make all the wrong decisions.)
After that night, Lily experiments with using her wand as a knitting needle. Thinking about family, or friends, or even just the vague thought of Protect the wearer makes others like her multi-colored sweater. Thoughts of Snape, or Voldemort, or the Death Eaters turn a completed project prickly to the touch, and Lily uses this to give several Slytherins some truly terrible burns around their necks, from when they had all put on the matching sweaters that had appeared one morning.
(The Marauders never figured out it was her.)(Sirius suspects something though.)
Soon enough, all of Lily's friends are sporting knitwear, from hats to mittens to scarves, and even a blanket when she celebrates Marlene and Dorcas finally getting their act together. Even when the weather warmed, Lily kept knitting. All her friends knew how badly she needed to knit, and never turned the gifts down.
(Secretly, they all knew it was just as much because they needed the emotions in those gifts as badly as Lily needed to knit them.)
The night after James had asked her out for the final time, Lily had knit a scarf and poured all her emotions into it. The next time she put the scarf on, she felt a rush of Love, Friend, Protect, Cherish, Love, Excitement, Fear, Amusement, LOVE.
(Peter found her on the couch last night, having been slipping out to think about a gift for Marlene's upcoming birthday.)(They never talked about it again, about how Peter had pet her hair and told silly stories until Lily stopped crying, and reassured her that James loved her just as much, and that she wasn't silly for wanting to be more than friends when they could barely even manage that.)(Merlin knows he had just spent four hours convincing James that this was real and that Lily had said yes.)
After that, Lily bought a small case and put the scarf away in it, with a label reading "I finally said yes."
(Different scarves were added to that box over the years, some happy and filled with love, others filled with pain and sorrow and a loss so powerful that the normally beautiful calligraphy was nearly unreadable from shaking hands and salty tears.)(As much as it hurts, Lily pulls that one out the most, to remind her of the family she had lost, and the reasons she was fighting in this war.)
The Order had laughed when the newest Gryffindor graduates show up to their first battle in muted black and brown sweaters and knit caps. They poke fun at the kids for thinking some yarn would ever keep them from being hurt. The newest members take the ribbing with good grace and secretive smiles shared with Dumbledore and Lily.
(The Headmaster had seen what sweaters knitted by this particular young woman could do.)(The Order stopped laughing when a blood-boiling curse shot by Bellatrix Lestrange washed over her cousin's chest like only so much water before he returned spellfire.)
Lily knits protective jumpsuits for Harry once she's pregnant, she knits sweaters with runes meaning Home, Family, Love for Remus when he goes away to the werewolves, she knits earmuffs with silencing runes on them for Sirius when he mourns his brother, she knits James a scarf stuffed to the brim with all the love she could pour into it, she knits a hat with confidence runes for Peter when he's scared to be their Secret Keeper.
As soon as the door opens on Halloween, Lily regrets every single thing she ever gave Peter. In that moment, though she doesn't know it, everything she had ever knit Peter turns slightly prickly and the emotions fade. The next time he tries to wear one of the things she gave him he cries because what used to be a rush of warm emotions is now barely a trickle, and the sweater is uncomfortable and itchy where it used to feel like the softest of silks.
(Peter wears it anyway, as punishment for what he's done. Lily and James were his family and he had betrayed them.)(As far as he's concerned, he deserves much worse than an uncomfortable sweater and the life of the cherished pet.)
Years later, in the weeks after the Battle of Hogwarts, Harry finally goes through the wills of his parents, uncles, and Pettigrew. He finds apologies, and I love you's, and "I'm so sorry we had to leave you behind my love."
In Pettigrew's will, in a postscript, he finds a note.
Harry, it reads. I know that I have done the worst thing a person can, and that is to betray their family. I don't expect you to forgive me when I will never forgive myself, but I thought you should know: your parents loved you more than anything else in the world. Your dad made bubbles for you to play with and let you ride around on his back, and your mum danced around the kitchen with you when you were sad. The sound of your combined laughter is one of the most cherished memories I have. But there was something else: your mum loved to knit, and she put something special into everything she made.
Below are the locations of everything Lily knit that I could find. I would direct you especially to the largest blanket and the wooden box. The blanket was for you, when you were born. Lily knit non-stop for almost a week to finish it, and made it as large as she could. She wanted you to be able to use it long after you had grown. When you wrap it around yourself, take a deep breath. The blanket still smells of your mother with all the charms she laid into it, and the feeling of it around you is your mothers hug. I could never figure out how she did it, but Lily was brilliant, and I will forever regret my part in killing that brilliance.
In the wooden box are scarves of every design and color. Each one is labeled in order. When you wear those scarves, you feel what Lily was feeling when the events happened.
I wish I had more to give you Harry, but the small amount of gold I have is going to a charity for war orphans in your name, and the name of Theodore Lupin. Raise him well Harry. For Remus, and Lily, and James, and Sirius, and the parents they never got to be. And maybe for the little boy that would never think to betray his friends beyond stealing a chocolate frog.
I'm sorry.
Peter Pettigrew
(Harry cried after reading the note. And after finding the blanket. And after wearing his mother's scarves. Really Harry just cried a lot in the following days, but instead of breaking him, each tear helped heal rips in his soul he hadn't realised were there.)
(Harry took up knitting, adding scarves to his own box and making things for his wife, brothers, sisters, children, nieces, nephews, friends, and the orphanages opened in his name after the war.)
(The blanket ended up on his bed at a refurbished Grimmauld, and Lily Potter's scarf box was put on a shelf in his office.)
(Ginny refused to have sex when the blanket was on the bed, saying it felt like his parents were watching them.)
(Little did she know, she was right. Lily had tied herself to the knit gifts she gave her family. As long as even one remained, so would she, and where Lily was, James was sure to follow, keeping watch over their son, and their grandchildren, and great-grandchildren, and all the generations to follow.)