Newton's First Law: an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

It had been a short, simple voicemail. Would you consider coming home for the weekend? Love you, Mum.

Sherlock had done something. Obviously.

The fact that Mummy hadn't even said his brother's name meant it was enough to make mentioning it around Father dicey. Probably suspended yet again, and for God only knew what. The fact that Sherlock hadn't been waiting with Father and Mummy to welcome Mycroft when he dashed in the front door chased by an early November deluge meant they were at the worst of Sherlock's stubborn backlash. He hugged his mother, shook hands with his father, made it a point to smile and meet both sets of eyes with bland reassurance. Father was tense, avoidant, all angles and clenched muscles. Mummy was wilting, a puddle of vaguely trembling limbs and worried eyes. Mycroft swept her with a second glance. Fragile smile, but none of the warning signs he knew.

Ah yes, home.

He hadn't missed it.

After depositing his case in his room, he came back downstairs to find Father's study door closed and a strident phone conversation leaking through it. Standard procedure, then. Mycroft turned left and headed to the library, where he could expect Mummy to be. She was sitting in the wingback chair closest to the door, sipping a cup of tea.

He smiled and drew a breath to speak, but she put a finger to her lips and cut her eyes to the third bookshelf to the right of the door. He nodded his understanding. Sherlock had retreated to the room behind the hidden panel and would be able to hear their conversation.

"Is term going well?" Mummy asked.

Mycroft poured himself the remaining cup of tea, spooned more sugar than he ought into it, and did not pitch his voice lower to match hers. "Fairly."

"Good professors?"

"Fenwick is a bore, but it's difficult to make microeconomics interesting at half past seven."

"No trouble."

It was meant to be a question, but she phrased it as a statement. Mycroft never had trouble, never caused trouble, never did anything but solve trouble.

He smiled as blandly as before. "Never."

They sipped their tea and watched the rain lash the window till the silence cracked with the waiting.

"What happened this time?"

She cut her eyes to the panel again, but Mycroft waited. He wasn't above smoking his brother out of his den.

"Well, he was taken to the headmaster's office because of some business to do with the mice in the laboratory."

Mycroft repressed a groan, but allowed himself to close his eyes to absorb this. "Extracurricular experiments?"

"Apparently," Mummy said. "Two dead, one in the throes when the class arrived."

"And they're sure it was –" Mycroft cut himself off and changed the question. "What poison did he use?"

Mummy shrugged. "They didn't tell me and I didn't want to know. That was only the first part of the story."

Mycroft squared his shoulders and nodded for her to continue. He thought he detected some noise from the other side of the panel, but he couldn't be sure.

"Well, while he was in the headmaster's office, he apparently… made some observations about the headmaster and his secretary that were…"

"Indelicate?" Mycroft supplied.

"Precisely."

A definite thump from the other room. Sherlock disapproved of the way the story was told, then. Mycroft had no sympathy.

"How long is he suspended?"

"A week, but they want to meet with your father and me before he comes back. It's the third time he's been suspended, and this is only his second year."

"Does Father know about the meeting?" Mycroft asked.

"He was the one who took the call."

Another wince. "And Sherlock is… alright?"

Mummy nodded. "He hasn't, you know. Not in a year."

Reassuring, but only barely. His father had a notoriously short memory when it came to keeping promises. Particularly when provoked.

The panel opened emphatically, though only just far enough to reveal Sherlock, wearing a t-shirt, flannel pjyama trousers, and a black robe that all looked rumpled enough to have been slept in several days running, and looking cross. He slid out of the secret room and closed the panel behind him.

"Sherlock, your brother came to visit for the weekend," Mummy said unnecessarily, beckoning him closer.

Sherlock, all gangly limbs and unruly hair, stayed where he was. Mycroft met his gaze, returning his cool assessment. They had not parted well when last they saw each other, something of a pattern since Mycroft first left for uni, and it seemed Sherlock was as capable of holding a grudge as he was of murdering rodents.

The rumples in Sherlock's clothing bore traces of splashes of something, and his fingers where he was fidgeting with the dangling belt of his robe were reddened. Mycroft could have deduced he was experimenting with something without the physical evidence, but on what remained more of a mystery. Some irritant, to be sure. He shifted his chin toward the secret panel, raising his eyebrows a fraction. Sherlock's nostrils flared in defiance. Mycroft cooled his eyes, letting the lids settle slightly. Sherlock quite frankly didn't care enough of what others thought of him to be secretive, so the use of the room was a surprise. It had been Mycroft's preferred haunt when he lived at home because Mummy would have considered it an imposition of privacy to venture within, and Father never went in search of anyone. They came to him. For Sherlock to be silently forbidding Mycroft to enter was… uncharacteristic.

"Well, I should see if dinner is almost ready," Mummy said, if possible deflating even further. "Your father will be hungry."

She put a hand on Mycroft's shoulder as she passed, but her eyes stayed on Sherlock.