A/n Hey there to anyone who's still around! This is that flashback chapter that takes place during the Holmes' children's childhood. It's after Victor Trevor but before the burning of the Musgrave Hall ancestral home. It'll likely be a two-parter. The ages of the children are: Mycroft, 18; Eurus, 13; Margaret, 12; Sherlock, 11.

———

ᴛʜᴇ ɪɴᴄɪᴅᴇɴᴛ ᴘᴛ. 1

Mycroft watched from afar as his two sisters ran along the beach, kicking up sand and pushing each other into the undulating waves as they hit the shore. He spotted his brother under the seclusion of a beach umbrella, his nose stuck in a book.

"Sherlock!" Mycroft called out, walking over to the boy.

Sherlock raised his head slightly, his knuckles whitening around the book upon Mycroft's approach. "What?"

"Wouldn't you rather be playing in the sand?"

There was a prolonged pause. "No."

Mycroft narrowed his eyes, knowing it would be useless to press. His brother was too stubborn.

It was after the disappearance of Sherlock's very dear friend that his brother had become increasingly reclusive. Mycroft couldn't help but think that their sister Eurus was behind this, as much as it sickened him to indulge the notion, she was the last person to see Victor Trevor alive. Yet, barely a week after Victor had gone missing, Sherlock was depressed and Eurus was enjoying herself by frolicking on the beach with an ignorant Margaret.

Mycroft wondered if Margaret was also involved with Victor Trevor's disappearance. With only a year separating them, Eurus as her senior, the two sisters were attached at the hips. It worried Mycroft as he knew that Margaret was intelligent and genuine. Though when with Eurus, the pair would get up to all sorts of mischief. He recalled last week when their parents received a call from a primary school teacher to inform them about the sisters physically bullying other students.

Mycroft had tried to appeal to their parents concerning Eurus' behavior, especially after Victor's disappearance, though they were reluctant to seek professional help. In the meanwhile, Eurus received a lecture and her behavior didn't change. She and Margaret continuously acted up. Sherlock began to grow silent, avoiding his sisters to the point of eating dinner in his own room. Mycroft began to spend more time at home, concerned that his sisters were picking on Sherlock behind his back.

———

It was a chilly evening at the Holmes residence. Mycroft split his time between tending to the fire and stirring the pot of stew that he'd made for dinner. A crossword sat on the kitchen table and every time he passed by it he linger long enough to complete a puzzle.

Overhead, footsteps thundered along the floorboards. His eyes snapped up in distaste hearing Margaret and Eurus run down the halls. Throughout the night they'd been nothing but trouble. It began with their parents leaving for Glasgow for a wedding. Mycroft agreed to watch his siblings for a few days, knowing he'd regret managing two in particular. The sisters, believing they had free reign of the house now that their parents were gone, began causing total chaos. Mycroft had scolded them multiple times to no avail; he began thinking he needed to be more forceful.

An opportunity suddenly arose as he heard something shatter upstairs and a single laugh echoed down the stairwell. He cocked his head in its direction, his jaw setting in annoyance.

He decided to confine them to their rooms until they calmed down. Perhaps he would keep Margaret downstairs with him instead? Separating them seemed a good idea as he arrived at the top landing to find a picture frame broken, Margaret at least had the decency to look ashamed. Eurus twisted her hands behind her, pressing her lips together to prevent a smile bursting onto her face. Down the hall, Mycroft spotted Sherlock peeking through his door and offered the boy a subtle nod before turning his attention to the girls.

He began in a stern tone, "I am extremely frustrated with you two. I've asked you to not cause trouble while mother and father are gone but it seems you can't listen." He nodded pointedly to Eurus. "Go to your room until dinner is done. Margaret, come downstairs with me." Margaret started toward him though Eurus lashed out, gripping her sister's hand.

"No!" Eurus exclaimed.

Mycroft raised a brow at his defiant sister, she was wearing on his last nerves. He reached forward to pry them apart and Eurus abruptly jerked Margaret back. Alarm flashed through him and he snapped a hand out to grab Margaret's free wrist, hoping Eurus wouldn't lessen her grip on the other side, before the pair reeled barefooted onto the shards of glass. To his shock, Eurus' hold slackened and Margaret slammed into him. She immediately distanced herself, prying his fingers from her thin wrist.

Simultaneously, Eurus landed on the glass. Shards sliced and cracked under her feet, springing water to her eyes. The girl fell to her bottom, silent tears running down her cheeks. Mycroft rushed past Margaret who stood wide-eyed in the hallway, to examine Eurus' injuries.

As his fingertips hovered over her skin, Eurus recoiled at Mycroft's proximity, her pain turning to anger. As he looked up in surprise from her withdrawal, he was able to dodge a piece of glass being slashed at his face. He fell back on his palms, staring at Eurus bewildered. The shard clutched within her hand drew blood that leaked out of her closed fist, a startling scarlet.

Mycroft gathered himself enough to inch closer to Eurus, holding up a calming hand. "Eurus, put down the glass."

She shook her head rapidly, a smile breaking through. "No — I won't," she paused, "I'm not dumb."

He blinked. "I know that.

She hastened to her feet and Mycroft mirrored her, glancing behind him to find Margaret standing pin-straight. Eurus continued, "I heard you talking with mother and father about getting me help and moving me out." His gaze widened, he didn't want her to overhear that conversation which could easily be misconstrued. She turned toward him, her gaze broken, a complete turn compared to the laughter it held before. "Why are you trying to send me away?!".

Eurus looked over his shoulder to Margaret, locking eyes with her and shouted accusingly at him, "He wants to separate us Millie, we won't be able to play together anymore!"

Mycroft spun on his heel to face Margaret, taking a step toward the girl as she inched toward the first stair. "That's not true–"

He realized too late he never should have turned his back, perhaps it didn't occur to him that he was in danger as the person behind him was his sister. Though as he stepped toward Margaret and arrived on the landing, a figure pushed him hard from behind, knocking him off balance. His arms flailed above his head, his legs tripping over themselves as he tumbled downstairs. He can't recall if he came to a stop as it was impossible to discern between the sensation of the wood colliding with him and the throbbing pain that indefinitely lingered.

——

Mycroft was awoken to his body being frantically shaken. The light beyond his closed eyelids ached, and he turned his head away only for a shot of pain to fire up his spine, resulting in a pulsating headache. He groaned, squeezing his eyes closed tighter.

"Mycroft?" A voice whispered, their breath hot on his ear.

He flinched at the proximity, though recognized the owner and forced his eyes open. Over him sat a boy with a bountiful head of curls, his shockingly blue eyes were wide in fright and Mycroft noted to his surprise that they appeared watery; Sherlock rarely cried.

Upon seeing Mycroft's eyes open, Sherlock fell back on his knees, sighing in relief. Mycroft attempted to sit up though Sherlock rested a firm hand on his shoulder. His brother said, "Don't move, you just fell down the stairs."

Begrudgingly, Mycroft relaxed on the floor. He asked, "Where are Margaret and Eurus?"

Sherlock stilled at the question, it was as if the mere mention of them could set him off. He shrugged. "I don't know. I closed my door when the fighting started, then I heard a loud thudding noise. I waited until it was quiet and by the time I did you were like this," Sherlock gestured to Mycroft's situation, "and they were gone."

Mycroft pressed his lips into a firm line. This was not good. If their sisters ran away, who knows what could happen? Eurus needs help, and he's worried for Margaret if she's gotten dragged into this. Even if he just had a nasty tumble, he can't lay around and wait for something worse to happen.

Once again Mycroft tried to push himself up. Sherlock protested, and it wasn't until Mycroft tried to move his arm he grasped how bad of a fall he had. It was likely that his brain hadn't registered that the bone was protruding from his arm, though when he tried to move it — when he saw it, an overwhelming sensation hit him that left him crippled on the floor.

"I told you." Sherlock said. "The paramedics are on their way, don't move until then."

"I can't," Mycroft gritted out, "I need to find Margaret and Eurus."

Sherlock's mouth fell open and closed. He shared the similar quality of stubbornness with his brother, and watching as Mycroft still struggled to his feet despite the pain led the younger brother to believe the elder wouldn't rest until he knew their sisters were safe. Sherlock offered this, not knowing if it was a genuine promise or something to placate Mycroft, "I'll find them."

Something flickered in Mycroft's eyes. "It's not necessary for you to, I'm the eldest."

"You're injured," Sherlock insisted, "I'll do it."

Mycroft scrutinized his brother through the pain, and in the silence the sounds of sirens could be heard. He wondered why Sherlock would offer, knowing how much he avoided their sisters. Though if he was willing to help…

Mycroft sighed, nodded slightly. "Alright. Be careful, and don't stay out after dark. When you come home remember to lock the doors. I'll push to be released as soon as possible," he paused as a spike of pain inconveniently appeared, "though if I'm not home tonight call the hospital to check in."

"Okay," Sherlock's tone made it sound like he was being overbearing.

"This is serious." Mycroft pressed. "Don't take this lightly."

Sherlock nodded, and as he did the sounds of the ambulance rolling to a stop in the mud reached their ears. Moments later, the paramedics entered to take Mycroft to the hospital, and Sherlock was left alone in the Holmes' ancestral home.