Most of the people around Sherlock, assumed he wasn't scared of Moriarty. Intrigued by him, excited by their rivalry, sensible of the danger he represented, but not afraid. Mycroft knew different. Once, if it was only once, Sherlock had shown he valued his own life, enough to fear for it.
Sherlock hadn't taken long to come to him after his request they talk. Mycroft knew he'd given away his own fear, so obviously, but on this occasion, he didn't care if Sherlock knew he was terrified. In fact, he needed him to understand why.
"We have Moriarty in custody." He stated without preamble.
"What for?" Sherlock asked, barely raising an eyebrow. Mycroft recognised the practised stoicism well.
"The Adler case, officially. Unofficially, it's in the public interest we discover what he wants, by any means."
Sherlock knew better than to ask what that meant. He waited for Mycroft to go on. Mycroft was staring at his shoes, but his voice was calm as he explained.
"He's…obsessed, with you, Sherlock. He won't talk, unless it's about you and he doesn't need any prompting to do that. He's everything you already know; brilliant, psychotic, but now everything he is, is aimed at you."
Mycroft watched, as Sherlock wandered across the room and stared out of the window in silence.
"What happens next?" Sherlock asked, at last.
"We can't charge him. At the moment I'm contemplating a fatal accident."
Sherlock threw a disgusted glance over his shoulder. Mycroft shrugged.
"I've covered up worse corruption."
"That, I don't doubt." Sherlock replied, turning back. "But it won't work, he alone, is not the problem. His web won't disappear if he does."
Mycroft nodded.
"He isn't really what I wanted to talk about. I don't know what can be done about him."
Sherlock turned his head, but kept his back to Mycroft.
"Meaning?"
Mycroft took a deep breath, stepping towards Sherlock determinedly.
"Leave, Sherlock."
Sherlock visibly froze.
"There are limits, to his intelligence, they fall behind yours. There are even limits to his resources that might fall behind mine, but there are no limits whatsoever to his disregard for human life. His life and yours, most importantly. …Please, go somewhere out of reach, until he can be stopped."
Silence followed, the longest and most uncomfortable of Mycroft's life, Sherlock still staring out of the window. Had it not been for the one, single, entreaty, Sherlock would have laughed in his face.
At length, Sherlock turned and regarded Mycroft steadily.
"I'm afraid, brother, it's too late to run or hide."
He didn't qualify the statement further. Mycroft didn't argue. He knew what Sherlock meant, he couldn't leave his friends in danger and Moriarty's web was flung too wide. Suddenly the brothers were shouting at each other; Mycroft wearing a trench in his carpet and Sherlock smouldering a hole in it's middle.
"RATHER A BEATABLE DETECTIVE THAN A BLOODY MERCENARY MYCROFT!" Sherlock raged, as Mycroft attempted to explain, he couldn't win.
Mycroft wasn't offended, but it convinced him Sherlock didn't understand what he was asking. He wasn't trying to find a means of defeating Moriarty. What Mycroft had to prevent, was more selfish and more simple.
"HE WILL KILL YOU SHERLOCK!"
Sherlock fell silent. Not from his words, but the ringing terror in his voice and Mycroft didn't care. Mycroft turned away, fear, frustration and hatred welling up.
A moment passed, before footsteps on the carpet brought Sherlock in front of him. Then he said two little words that brought an end to any hope Mycroft had, of stopping him fighting Moriarty.
"Help me." Sherlock said, simply.
Mycroft just stood, staring at him. Sherlock glanced at his hand, clenched at his side, observing the bruises.
"Was it really that bad?" He asked, quietly.
There, under his dismissive blustering, was a moment of honest fear. He didn't want to know what Moriarty had said, to push Mycroft that far, but for a single moment, he let the thought visibly unnerve him.
Mycroft knew then, what he had to do. Helpless fear became his world.
"What do you need?"
"Our one advantage, is that Moriarty isn't going to shoot me." Sherlock rattled off immediately, brother gone, robot detective returned. "He's going to make this last. While he's playing his game, we can play too. We have to wait for him to commit a crime in progress, that he can be tried for."
Mycroft frowned. Sherlock knew Moriarty could fix a trial. His head started to ache as his heart couldn't sink any further. Sherlock knew if they could predict Moriarty, they were one step ahead.
"Tell me you're not suggesting what I think you're suggesting."
Sherlock smiled grimly.
"Mycroft, give him the information he wants, then let him go."