Three years had passed since Sherlock had rediscovered his sister. He still visited faithfully, twice a month, always bringing his violin with him. They had made a lot of progress in connecting with each other. Where Eurus had initially shown no reaction at all, she would now play regularly with Sherlock, and sometimes speak with him. She never spoke to anyone else.

Mycroft had been terrified when he found out. He was convinced Eurus was planning to manipulate Sherlock in some way. Sherlock had been angry and defensive, saying he could take care of himself. Nevertheless, Sherlock had reluctantly agreed to allow Mycroft to review the recordings of their conversations on camera, after each visit.

Mycroft himself only visited once a year, on Christmas, and only because he was strong-armed into it by Sherlock and the Holmes parents. Both Mummy and Dad had reprimanded him for not visiting more often, but he wouldn't concede to more contact. Even Sherlock had mentioned something about "brotherly duties," but Mycroft had just looked at him coldly and told him, "She has you for that."

Now Sherlock and Eurus were playing a duet, one of Eurus's own compositions. The melody was rich and complex, tinged with melancholy and angst, just like Eurus herself. Sherlock finished playing and put down the bow, sighing as he did so.

"You are unhappy," Eurus observed. So today she wanted to talk. She would always be the one to initiate a conversation. If Sherlock tried, she didn't respond. The detective wondered if it was a question of control, as there were so few things in her life that she had any control over.

"Yes, I am."

"Something is wrong. With someone you love." She emphasized the last word, rolling it around on her tongue as if it tasted foreign. Which, to Eurus, it very likely was.

Sherlock could detect a hint of bitterness in her voice. For all her brilliance, Eurus had never learned simple social concepts like sharing. She wanted to have Sherlock all to herself, and was displeased when he showed affection to anyone else.

"Yes."

"But you said you love me. I'm your sister." She was probing, testing.

"Yes. And I've told you, a heart is expandable. You can fit more than one inside. I love Mummy, and Dad, and you, and John, and Molly. I loved Mrs. Hudson, and she still has a place in my heart, even if she's no longer alive."

"Who is it that's worrying you now? Wait, I know. It can't be someone you mentioned. Your voice didn't change at any of the names you mentioned. Is it Lestrade?"

"Actually, Greg is doing great. He's been recently promoted, and he's going to become a grandpa very soon." Sherlock smiled fondly.

"It's Mycroft, then," Eurus said matter of factly. She had likely known that the moment she saw Sherlock.

"Yes," said Sherlock softly.

"You never talk about him when you're here," she added.

"No."

"Because you think I hate him. You don't want to get me upset."

"I don't know, Eurus. You tried to get me to kill him. What else should I think?"

"You forgot about me, but you still talked to him," she said, her expression so very nearly pouting that Sherlock was alarmed.

"Remember what I told you, Eurus? The heart defies rational explanation. Loving someone doesn't decrease your love for someone else. I can talk to Mycroft, and I can talk to you. I can enjoy John's company, and I can enjoy yours, too." Sherlock gazed at her sadly. If she had understood that concept all these years ago, perhaps she wouldn't have killed Redbeard in a fit of jealousy. Or she might still have. Eurus was broken in a way Sherlock would never understand.

"Mycroft is ill," she deduced, and Sherlock didn't bother asking her how she deduced. He wasn't in the mood for playing deduction games. "It's chronic."

"Yes, he is. It's aplastic anemia. The cause is unknown at the moment, but it doesn't matter much. The anemia is very severe at this point, and he has been hospitalized."

Eurus didn't react to the statement.

Sherlock continued. "Eurus, you know, if he doesn't make it, I'll be very upset."

"You'll still come?" she asked flatly, assessing him with a piercing glance.

"Probably. I might not always feel like playing, however," he answered honestly. Plunging further in, he added, "For most people, losing someone they love breaks them, and to a certain extent, they never fully heal."

Eurus was thinking silently. "Does he need a bone marrow transplant?" she asked curiously.

"That's his best chance. Of course, you know who makes the best donors."

"Siblings," she answered promptly.

"Yes. You know, Mycroft saved my life many times. Whether it was the drugs, or Moriarty, or imprisonment, he did his fraternal duty. It is about time I repay some of the favors. I like when things are balanced."

His sister regarded him coolly. "You can't, can you?"

"No, I can't. It's ironic, isn't it?" Sherlock's voice was now tinged with bitterness and self-recrimination. "The very thing Mycroft has always tried to keep me from, has now ruined his chances for recovery. The years of drug use have left their effects, and I'm now in no condition to be a donor."

"You want me to do it."

Sherlock leaned very close to the glass and looked at his little sister soberly. "Eurus, this isn't something anyone can force you to do. The decision is up to you. You are very clever, and understand all the ramifications of such a procedure. You're putting yourself at risk, however minor. If you'll do it, it will be purely your decision."

"Why would I do it?"

"I have no clue," Sherlock said honestly. "What do you think?"

"Let's say Mycroft dies. That will change things, won't it? You won't be the same." She paused. "You probably won't be allowed to come visit anymore. There's a very strict no-visitor policy here, you know. Only Mycroft can make exceptions."

"Oh," Sherlock breathed, feeling stupid. Of course it was only his brother's influence that allowed these visits.

"Also, Mycroft himself will stop coming, obviously."

"Mycroft?" Sherlock asked in confusion.

"Not his Christmas visits. When he comes around just to talk. About government matters, and scientific breakthroughs, and things like that."

"Mycroft comes?!" The Holmes brother asked in astonishment.

"Only when others aren't around. He doesn't like feeling pressured by the expectations you all have of him. He won't come here to say all those sentimental things you want him to say. He won't suddenly express his love, or give apologies. He won't tell me how much he misses me, or how happy he is to see me, etc. etc. etc." Eurus mimicked all the sentimental expressions with disdain.

"But... why does he come at all?" Sherlock asked.

"To talk. He likes to discuss things with me, and get my opinion, since I happen to be clever."

"You don't think it has anything to do with... sentiment?"

"Of course it does. Mycroft has always suffered from sentiment, but doesn't want to admit that to himself. Nevertheless, his sentiment hasn't made him completely stupid yet. Except when it comes to you, of course."

The detective mulled this over. "So how do you feel about saving his life?"

"I think I'll do it. It's not a matter of how I feel. I don't act based on sentiment, only cognitive reasoning. I will benefit from it by having your continued visits, as well as his. He will also owe me another favor."

"No Moriarty, this time," Sherlock sighed.

"No, he wouldnt do that again. I want a baby grand piano"

"Oh?"

"Yes. I want him to come play with us. Duets are getting boring. I want to try adding a piano, next time."