A/N: Remember that time when I said that this fanfic would be alternating between chapters of Will and Cecily when they were kids and when they're teenagers during the ID stories? Well, I wasn't able to think of an idea for the next child one, which is why this story is only just being updated now, with an ID Will and Cecily. So, if you have any prompts for me to work on, all suggestions would be greatly appreciated.

Disclaimer: Cassandra Clare owns The Infernal Devices.

The four of them gathered the library as night fell. It was Halloween night, and they were going to be having some fun.

"So what's your plan, Will?" Jem asked. "It was your idea, so I assume you must have something in mind."

"Come on, James, you've spent enough Halloweens with me to know what I have in mind," Will said briskly, blowing out the match he'd been using to light a few candelabras. They lit the small alcove the four were tucked in well enough, but past the outer edge of light was just the dark shadows of the bookshelves. "First in order are some treats."

From under the table, Will brought out a tray of small candied apples. "Tessa, here's yours. Cecily, yours. And Jem. It took me a long time to make these all, so eat them up."

Tessa raised an eyebrow before tasting it. "You made these yourself? I wouldn't have thought you a chef."

"What can I say?" Will shrugged. "I'm a man of many talents."

The apples disappeared quickly, and then they all looked expectantly at Will. "Now it's time for stories. Every good entertainer has one that's able to scare some people. Cecily knows one, don't you?"

Cecily grimaced. "Don't make me, Will."

"I'm not taking no for an answer," Will said stoutly. "Right here next to me, now." He moved over a little to make a space.

As Cecily got up, her brother smirked at her. "I'll be right here."

"Shut up." Cecily sat down in front of Tessa and Jem, Will close by.

"This is an old story we used to hear in Wales," Cecily began. "Will told it to me on my seventh birthday (it wasn't even Halloween, so I don't know what he was thinking)—" she gave her brother a menacing look "—after I received a present that the characters in the story also get. Scared me to death first time I heard it.

"There are three girls, triplets. When they were babies, their mother would sing this lullaby to them." And Cecily sang in a clear voice,

"Heno, heno, hen blant bach,

heno, heno, hen blant bach.

Gwely, gwely, hen blant bach,

gwely, gwely, hen blant bach.

Fory, fory, hen blant bach,

Fory, fory, hen blant bach."

The last note echoed throughout the library, hanging in the air like a drop of water on a branch. They waited until the sound had thinned and wavered out. Tessa shivered. She didn't know what the song meant, but the way Cecily had performed it, it had a haunting and eerie quality to it.

"Maybe the mother, after four or five years of singing it to her children, had made it a tradition to sing it at night, even if she wasn't singing it to the girls. So every night, they would hear from across the hall their mother singing this song.

"By now, the girls were approaching their seventh birthday. On the day of, they were presented each with an exquisite porcelain doll. Each one was a little different, different hairstyles, expressions, and clothing. The girls loved them. They spent the whole day playing house with the dolls and making games with them.

"When it was time for bed, the girls stood the dolls up on their dressers in front of their beds. As usual, they heard their mother singing.

"The children went to sleep. Late that night, one of the girls woke up to the sound of more singing. She thought it was odd, since her parent's room was silent. No one would be awake at that hour. Then she looked up and saw something impossible. It was the dolls that were doing the singing.

"The girl was enchanted; dolls singing! It was amazing. She quickly woke up her sisters to show them. The rest of the night they stayed up as long as they could, listening to the dolls.

"When it was morning, the girls had fallen back asleep, but as soon as they were awake, all they could talk about was what had happened the night before. Determined to witness when the dolls began to sing and see how long they sung for, the girls napped all day, so they'd be well rested during the night.

"Only something went wrong when the time finally came. The girls saw when they began, all right, around midnight. But they never knew how long they sung for. When the parents went to see them the next morning, all three were dead."

Cecily finished with a shudder. "That's the end—" She broke off midsentence and screamed, letting out a stream of fluid Welsh profanities, springing to turn around. Will had grabbed her by the sides and now stood laughing his head off, leaning against one of the bookshelves for support.

"Goddamn it, Will!" she cried furiously, after she had recovered. "Rot in hell, why don't you?" she gasped.

"Come on, Cecy; it's all part of the fun," Will managed between laughs.

"Ugh, I hate you!" Cecily pressed her hands to her head. "You know I don't like that!" Shakily, she made her way to her seat and glared at Will.

Will had calmed down now, but was still enjoying the moment. It reminded him of the tricks he'd play on her when he lived at home still. She'd spend the rest of the year plotting ways to get back at him, which usually happened around Christmas time. It was always worth it though, he'd thought.

Especially this year. He'd missed being able to pull pranks on people on Halloween, since the usual inhabitants of the Institute didn't startle as easily, being battle-hardened warriors and all.

Looking at Cecily's expression, Will sighed. "All right, all right, I'm sorry," he said. "You know how it is with us; we always used to do it." He got up and sat next to her. "Ella dull, all right? You said it never fails."

Cecily regarded him for a moment and the nodded silently. She reached behind to the back of her head and then parted her hair into two halves, leaving one part for Will and the other to herself. As Jem and Tessa watched confusedly, brother and sister began to braid Cecily's hair.

"What are you doing?" Tessa wondered.

"Something that calms me down when I'm worked up," Cecily explained. "My sister found out when I was younger that I would stop crying if my mother played with my hair a little. Guess it must be because keeps my mind off it. Still works today."

"And Will," Jem said slowly, awestruck. "When did you learn how to braid a girl's hair?"

"I was forced to learn to I could calm her down if I needed to," Will said. "Cecily was a bratty baby, you see, always crying."

He spoke like it had the greatest bore in the world to do, but in truth, he'd enjoyed it. It made him feel useful that he could make his sister happy again when she was upset, the same way he was feeling while he sat intertwining the threads of hair one over the other.

I'm not going to forget what makes you feel better when you're frightened, chwaer fach, even if it has been five years. No need to worry.

A/N: That nursery rhyme I just found on the Internet, so I apologize if it never existed in 1878. Fit the purpose, so there you go. Also, sorry if that "scary" story Cecily tells isn't scary at all…I hate horror so I have almost no experience with it and came up with that story right off the top of my head, and still got a little creeped out while writing it. Hence the shortness of the story.

Another reminder if you have any prompts for when Wil and Cecily were children, tell me, please!

Translations –

heno / tonight

gwely / bed

fory / tomorrow

hen blant bach / dear little children

Ella dull / Ella's method

chwaer fach / little sister