Sherlock acted like a five years old when shocked
"But he's your brother! He's been stabbed and now he's gone! Don't you care at all?"
"Of course I do, John, but that doesn't mean I should be screaming in panic, does it?"
"...I, sorry... sorry for screaming, Mycroft, but..."
"Ask Mrs. Hudson to make a cuppa for you, will you John? Now if you'll excuse me, I have something to take care of."
Mycroft hung up the call and went inside his flat. He went to the bedroom and knelt down beside the bed. He lifted the bedcover.
Under the bed was sherlock, curled down like he did twenty years ago, the first time someone had shouted "freak!" at him.
"Hey," Mycroft said to him.
"Mycroft," Sherlock said as he crawled out. Mycroft noticed the blood stain on Sherlock's shirt. Not really deep, but it won't do him any good to delay treatment any longer.
"The bad guy stabbed me!" the younger brother talked as he climbed into the older's embrace, "that stupid crook! He pulled that knife out of nowhere! I... I..."
"Ssh," Mycroft hugged him as he trembled and sobbed. He called for 999 with one hand and tried to calm Sherlock down with the other. After he finished the emergency call, he turns his attention fully on Sherlock. "It hurts!" sherlock cried again. "Sherlock," Mycroft called his attention, "recite the periodic table for me?"
Taken by surprise, Sherlock does so. "Hydrogen, helium, lithium..." until the siren of ambulance was heard.
"Mycroft?" sherlock said timidly, sounded a bit like five years old child.
"Yes, Sherlock?"
"You find me."
"Always, baby brother."
Sherlock nudged his forehead against Mycroft chin, and he kissed it before the paramedics took the younger brother away.
Mycroft cared, Mycroft protected, Mycroft always found Sherlock. This time wouldn't be any different as he took his mobile phone, determined to personally take care of anyone who hurt his little brother. Just like usual.