John plodded up the stairs of 221b Baker Street, exhausted and relieved that his day was nearly over. Another couple of hours and he could relax, drink a beer, and watch some telly. But first, Tuesday dinner.

They had created a tradition of sorts when the flat had been in the works of rebuilding. Every Tuesday, they would have dinner. At first it was takeaway trays crouched amidst the rubble, but now Sherlock actually went to the trouble of cleaning off the kitchen table for them to sit at, Rosie perched in someone's lap, and Mrs. Hudson worrying over portion sizes. It was good for Sherlock, too, because Tuesday was also the day he went to Sherrinford.

As John bounded up the stairs, he could hear Sherlock playing the violin. The melody was vaguely familiar, but he couldn't quite place it right off. By the time John reached the door and pushed it open, Sherlock had finished and was glaring at his phone.

"That song cannot be recognized as played. Please try again."

Sherlock made a groan of annoyance and slammed the phone in his desk drawer.

John cleared his throat and closed the door. "Interrupting something?"

"Eurus," was the clipped, short answer he got before Sherlock started pacing. He didn't say anything; Eurus was still a delicate subject at times.

After a moment, Sherlock began elaborating. "I went to visit her, and she was playing this song. I asked her what it was, and she just smiled at me, and kept playing it. She never did answer me, and now..."

"You've got a song stuck in your head." Yes, this could be problematic.

Sherlock yanked the drawer back open. "I recreated her performance, but the phone doesn't recognize it. Do you?"

He shoved the phone into John's hand, and the melody from a few minutes before played again. This time, he realized why it sounded so familiar, and also why Sherlock would never have been able to place it.

John had his mouth open to say yes, he knew good and well what song this was, but seconds before he spoke, he had another idea. An evil idea.

"No idea."

"What?"

"Sorry. No idea what that is."

Sherlock groaned in frustration again and John took the opportunity of his turned back to hide a snigger.

"Well. I only came over to see if you needed me to pick up anything for tonight. You weren't answering your phone. I guess I know now why."

"Tonight? Oh, is it Tuesday? Mrs. Hudson's been to the shops, I'm sure she's gotten everything."

"Right. I'm off to Molly's for Rosie."

"Yes, yes, I'll...Did you say Molly?"

John was almost to the door. "Yeah. She has Rosie today."

Sherlock was already in the process of pulling on his coat. "This is excellent. Molly has a far superior knowledge of pop trivia than you do."

"Oh, so you're..." John was pushed past, and Sherlock halfway down the steps. "Coming with me."

While Sherlock's attention was focused on finding where John had parked, John quickly pulled out his phone. He made a group of his most recent contacts, with a couple of extras thrown in.

sherlock could come round asking about a song pretend like you dont know it

SEND

XxxX

Molly was a thirty minute drive away, plenty of enough time for Sherlock to come up with the theory that his mystery song might be on any given radio station. It only took five minutes for John to begin regretting his choice of pranks.

"She's been a perfect angel. You should know, she's off carrots."

John ignored Sherlock bouncing over his shoulder. "What? She loved carrots yesterday."

"It's sweet potatoes now."

"Yes yes yes yes. Hello, Rosie."

Sherlock swooped in a kissed her very quickly on the forehead. "Do you know this song?"

He pushed the phone into Molly's hands, who looked confused. "What?"

"Song. Listen."

She held the phone close to her ear. "Erm. I'm sorry, Sherlock, but no. I don't know this song."

Sherlock took the phone from her with a muttered grumble that may have been along the lines of questioning their usefulness to him. He took off down the entrance way, and a moment later, John and Molly could hear the sounds of a cab pulling up and then away again.

They both broke up into giggles. "Oh my...Does he really not know…"

"It's been deleted from my hard drive!"

They giggled for a few more minutes, Rosie joining in happily.

XxxX

"You what?"

Sherlock set the phone on Detective Inspector Lestrade's desk. "I need you to identify this song," he repeated slowly.

"Well, I'll do my best. Gotta admit, though, I'm not quite what you'd call..."

"Just...Listen."

Lestrade leaned across his desk, resting on his elbows, and looking far more amused than the situation strictly called for. "Is it Chopin?"

"'Choppin''? No. No, it is not..."

"Donovan!"

Sherlock groaned. "Oh no, don't..."

"Yeah, boss?"

A displeased look crossed her face. "Freak."

"Sergeant Donovan. You look very….professional, today."

It was the most polite he could manage at the moment. "Thanks."

"Sherlock has come to us for help, Donovan. Listen to this."

He grabbed Sherlock's phone after noises of dissent from both parties, and tapped play again. "I dunno. Chopin?"

Sherlock breathed deeply, in and out a couple of times and reached for the phone. Lestrade pulled it away, though, with a quick whistle. "Oi! Anderson!"

"Oh, for the love of…."

"Yes? Oh, hi Sherlock. What can the Scotland Yard do for you?"

Donovan grumbled something under her breath that sounded a little profane and biologically impossible.

"Anderson, Sherlock is trying to find this song. It's important, see. I want you to listen and tell us if you know it."

Luckily, Sherlock was too distracted staring at the ceiling tiles in frustration to notice the big wink Lestrade gave Anderson. "Er. Yes. I'll do my best."

A moment later he guessed, "Chopin," and Sherlock snatched his phone away.

"Urg, just….Thank you, for your 'help', Grendel."

"Greg!"

They waited until Sherlock had disappeared into the lifts before they dissolved into laughter.

he's on his way to you next GL

XxxX

"I'm afraid I don't understand."

"Eurus implanted my brain with this insipid...melody, and I'm certain the only way to remove it is to identify it."

Mycroft stared at the phone sitting on his desk. "Well. I am, at least, thankful that our sister is using her considerable talents on this childish drivel rather than the alternatives."

"So do you recognize it?"

"Has it occurred to you..."

"Probably."

"Has it occurred to you, that Eurus made this song up herself, and you have been running about town on a fool's errand?"

Sherlock scowled. Yes, that had occurred to him. But some intuition told him otherwise. He took the phone back.

Mycroft would be no help.

XxxX

I'm sending you an email with an audio attachment SH

This is an urgent matter SH

is this you playing?

yes SH

its pretty but I dont know it. Have you had time to consider dinner?

XxxX

"You would know."

Sherlock stood in the newer area of the graveyard, looking down at the stone for Mary Watson. He came here when he needed quiet and some reflection. John didn't know. Couldn't know, at least not yet, not when they'd built up so much new trust.

This was still his fault.

John and Rosie came every Sunday, the tulips still rested where they'd set them.

"You would know. You'd laugh and ask how, with all my knowledge, I didn't have that song. You and John, you'd..."

The puzzle began to piece together. "You'd let me go crazy trying to find this song. You would sit back and laugh and watch."

He couldn't help the laughter that came out, although he did try to keep it quiet, only imagining the look on John's face if he caught him with the giggles in a graveyard only made him laugh harder.

Sherlock kissed his fingertips, then pressed them against the marker. "Thank you Mrs. Watson."

He then pulled his coat around him tighter and left.

Sherlock had a dinner to get to, and a prank to return.