It happened quickly, before John could stop him. Sherlock lunged and Mycroft didn't expect it, and the next thing John knew, Sherlock was sitting angrily in one corner of the room with a bloody hand and Mycroft was in the other corner, trying unsuccessfully to stop his bloody nose with a handkerchief.
Mycroft tried to wave John away, but finally acquiesced and let John give him a towel and inspect his swollen face. "Don't fret over me too much, John. I know that I definitely had that one coming." Sherlock snorted over in his corner and was holding his hand. He didn't speak, but stared at John and Mycroft and then went back to his sulk, curls falling in his eyes making him look the total role of the picked on little brother.
John managed to get the bleeding stopped and pressed gently on Mycroft's face. He hissed in pain softly as John touched a tender spot. "Yeah, I definitely think you broke it. You're going to want to get that checked out and treated." Mycroft nodded and made it up to the chair, dabbing at his face again with the towel. He pulled out his phone from his pocket and sent out a quick message. Almost immediately he got a response, and Mycroft soon ignored both Sherlock and John and was focused on his mobile.
John took that as a good sign, and made his way over to Sherlock, who was still sulking in his corner. He was still angry, but held out his hand for inspection when John wordlessly pointed. Although Sherlock made no sound, John could tell that the detective was in pain when John pressed a little too hard against the knuckles on his hand. "Yeah, it looks like you may have broken something too. You're going to want to get that looked at as well." Sherlock opened his mouth and John continued. "And not just me, you berk." A doctor at a hospital that can fix that hand and give you pain meds that are legal. And don't argue for a change. Just do what I damn say for once." Sherlock shut his mouth and went back to scowling.
Mycroft slipped his phone in his pocket. "I will be off for now, Gentlemen. Thank you, John for your care, I'm off to get this looked at now. As for you, brother, I fully accept your act of violence towards me, and I will admit, I deserved that punch and so much more. Until later." And then he was gone down to his waiting car.
John stared after Mycroft, shook his head and turned his attention back to his pouting consulting detective. "Well, come on, get up. We're going to hospital too. And no fussing. We're going.
"
Sherlock got up silently with John's help and waited patiently by the door as John grabbed his coat and keys. And Sherlock's complicity, John thought later, should have been a huge red flag that there was a huge storm brewing in Sherlock's mind palace.