I told him, was all Mycroft could think as he stalked into his house with a headache. If he had told Sherlock once, he had told him a thousand times, do not break the law—especially a federal law—to solve a case. And yet, here he was, back from the third meeting with the court this month and a very long day of pulling strings, paperwork, and pasting on a polite smile as he explained yet again why Sherlock should be set free. If it weren't for the fact that his legwork proved useful, Mycroft might have been inclined not to bother. But if he didn't, he'd have their parents to answer to. Lord knew that was a nightmare he didn't want to relive.

Why couldn't he just listen? Mycroft thought with an eye roll as he collapsed into a chair. He was getting too old for this and he wished there was some way he could imprint the message into Sherlock's head without simply shouting at him again. Honestly, was listening to his advice really so hard? Why did Sherlock always have to do the opposite of whatever Mycroft asked?

Opposite. Mycroft's mouth twitched at the corners. Oh. Now there was an idea. His lined mouth grew into a smile as he pondered the matter, and the more he thought, the wider his smile grew.

He had an idea. A wonderful idea. A wonderful, clever, ingenious idea.

It was several weeks before Mycroft could acquire the perfect box. He'd been searching foreign markets and had arranged for several additions and security layers to be custom-made. Now it sat before him, gleaming and sparkling in its perfection. The color was a rich dark wood that had every aspect of fine craftsmanship. It was small enough that he could easily carry it around, yet large enough that it could believably hold something important. The lock was strong and made for one key and one key alone; no skeleton would open this box (a theory Mycroft tested himself). There was a false bottom and several secret compartments that could only be discovered by the most observant of eyes. Best of all—and this had been the really difficult part—the box was designed with the type of technology that would conceal its contents even from an x-ray. It had cost him a small fortune, but he had a feeling it was going to be well worth it.

Now that the box was finally here, Mycroft took painstaking care to set the box in his office where it would be noticeable but not too much so. He turned it so that the lock just barely faced the visitor's side of the room. He was tempted to polish it so it would be extra eye-catching, but that would be too obvious. Last but not least, he proceeded to place absolutely nothing inside.

Everything was ready. As Mycroft sat down at his desk to wait for Sherlock, he found himself nearly giggling in anticipation and had to sternly rebuke himself a few times. Fortunately, by the time his little brother entered the room, he had quite regained his composure and replaced his slightly giddy smile with his usual mocking one.

"Hello, little brother," he said. As always, Sherlock didn't return the greeting and instead asked what he wanted. He stood behind the chair Mycroft had pulled out for him, apparently thinking if he could look down on him, it somehow made him superior. He really could be so silly sometimes.

"Another puzzle for you, dear brother. One that's far too sensitive to be discussed in your little flat." Sherlock turned his head. So far so good. Insulting his living space would get him in the contrary frame of mind Mycroft needed.

"No," Sherlock said. Well, this was working better than expected. "Sorry, don't have time."

"I can promise you at least a nine on your scale of interest." He felt a bit bad lying about that—the case he'd made up was barely an eight at best, but he had to get Sherlock in his office somehow. Sherlock looked back. Now was his chance. As Mycroft began to explain the details of the fake case, he subtly but not too swiftly let his eyes flick to the box. By his calculations, over 30% of his speech had been directed toward it. Just 10% ought to make Sherlock suspicious.

"Will you do it?" he asked, trying to sound polite.

"What for? I've no doubt you've solved it already," Sherlock said, but now he was starting to notice the box too, probably thinking it hadn't been there before. Good. His interest was piqued.

"Mostly, yes, but there are a still a few loose threads I'm still not quite clear on." Mycroft had to be careful now. If he was too pushy, Sherlock would know something was up. Worse, he might leave.

"And why me? Why not one of your little spies?"

Mycroft smiled and rested his chin on his hands. "Because I wouldn't feel nearly as safe taking them into my confidence." Before Sherlock could respond, Anthea knocked on the door—right on cue. Mycroft beckoned her in, and she handed him a file.

"Some important documents for you, sir," she said, and bowed her head before she left and shut the door. Mycroft got up from his desk, moved the box aside, placed the papers down in a tray behind it, and moved the box back.

Come on, little brother. Take the bait.

"Is that where you keep all your top secrets?" Sherlock asked, but only half-jokingly. Mycroft barely hid a smile. He was definitely curious.

Taking care to deliver the line perfectly, Mycroft turned to him and said with a polite but serious smile, "The contents of this box are no concern of yours."

Like clockwork, Sherlock arched an eyebrow and sat up straighter, glaring a little and turning his gaze onto the box. It couldn't have been more obvious he was trying to deduce its contents. "Oh really?" he asked.

"Yes, really," Mycroft said.

"Interesting. You just said you feel safe taking me into your confidence and now you're keeping secrets from me." Sherlock's head tilted as he spoke, a sure sign he was getting annoyed.

Mycroft hardened his pasted smile, though it was getting harder to keep from laughing. "What I keep inside of that box is none of your business. Now, shall we get back to the case?"

He explained the rest of it, and Sherlock half-listened. But Mycroft could see his mind was still on the box. His fingertips were pressed together and he stole more than a few glances toward it. Just as he had left to go and before he was out of earshot, another of Mycroft's aids came in on schedule.

"Is this the box you spoke of, sir?" he asked.

"Yes," Mycroft said, noticing with satisfaction that Sherlock's ears had perked up and he had slowed his walk just outside the office. "I want every precaution taken to ensure its complete security."

"Yes, sir. Do you mean it to be secret from everyone?"

"Absolutely everyone. Especially," and here he lowered his voice and watched Sherlock lean in against the door where he thought Mycroft couldn't see. "My brother."

"Oh?" the aid said.

"Make sure of it," Mycroft said, looking stern. He added extra emphasis on his next words. "I assure you, if Sherlock Holmes were to get ahold of what I've kept inside this box, it would change his entire life."

Sherlock's footsteps resumed and quickened. Mycroft stepped outside the office and put a fist to his lips, trying to stop himself from shaking with suppressed laughter as the aid began to secure the still-empty box.

It was stolen even sooner than Mycroft expected.

That was impressive, given how thoroughly he and his aids had safeguarded it. But then Sherlock did surprise him sometimes. Once this little game was over, Mycroft would have to find out where the flaw in his security was. But for now, he secluded himself in his private bedroom, turned on the feed from his cameras in Baker Street, and—as a rare treat—he sat on his bed with a bowl of gourmet popcorn.

"Let the show begin," he said to himself with a smirk as he set his laptop to show him the inside of Sherlock's flat. John was sitting in his favorite chair reading the paper, and Sherlock had just opened the door with what was clearly the box smuggled under his coat. Mycroft sat back and began munching on his popcorn. This was going to be quite amusing.

Sherlock breathed as if he'd run quite a ways, which was quite possible, and John lay down his paper and looked up at him. Sherlock grinned and held out the box. "Got it," he said triumphantly. "Took me hours of planning and a lot of stealth, but I've got it."

"Got what? What is that?" John asked.

"Whatever Mycroft is keeping from me," Sherlock said as he moved to the center of the living room and sat down at John's feet. Rather like a dog, Mycroft noticed. He set the box on the floor and put his hands together. "This was in his office, and he insisted on me not knowing what was inside. I reckon I've got about twenty-six minutes before he realizes it's gone."

Twenty-six? That was bloody insulting. Still, Mycroft supposed it was better to let him think that for now.

John rolled his eyes. "So you stole it from him so you can see what it is."

"Eey-yup," Sherlock said, and studied the box carefully. "Now the question is how to open it."

John got up from the chair, abandoning the paper, and sat down next to Sherlock. "Well, it looks like you need a key."

"Honestly John, your deductions improve every day," Sherlock said, and John sighed. "Of course there's a key, but if I know my brother, he'll have the only copy on his person, and there was no way I could steal it from him personally and not have him find out."

He was right about that at least, Mycroft thought as he fingered the key in his pocket.

"So then there's no way you can open it, is there?" John asked. "What's the point of having the box if you don't have the key?"

"Because there's always another way," Sherlock said, his eyes gleaming. Mycroft nodded. If there was one thing that made him proud of his brother, it was that he never gave up a case easily. Although in this instance, that was going to work against him.

He continued, "If Mycroft had really put all his hopes on the one key, then all it would take is for that one key to be lost or dropped or stolen, and whatever is inside would be inaccessible. He'll definitely have more than one way to open it."

Right again, Mycroft thought as he lay back on the bed and reached for more popcorn.

John picked up the box and turned it this way and that. He shook it gently. "It's pretty light. Doesn't seem like there's anything in it."

Mycroft froze mid-chew.

"Whatever's in there is probably inside a secret compartment," Sherlock said. "Even if it isn't, there ways of muffling the sound it would make so a person couldn't guess what's inside." Mycroft relaxed and swallowed. Sherlock retrieved his phone from his pocket and texted feverishly. "I just need to have a skeleton key made and then I'll be able to find out for sure."

John gave a short laugh. "Sherlock, are those even legal for private citizens to have?"

Sherlock raised an eyebrow. "Your point?"

John sighed and shook his head. "Did it ever occur to you to, I don't know, maybe not break into your brother's top-secret personal possessions?"

Sherlock glared. "No. He said whatever was in here would change my entire life, so it clearly concerns me. Therefore, I have every right to see it and he has no right to keep it from me."

"But what could it be?" John asked, pointing to the box. "There's only so much Mycroft could keep in there. It's probably just documents or something."

Sherlock shook his head, still texting rapidly. "If it were just documents, he wouldn't care if I saw them." He grinned. "It could be anything. Passwords to his accounts, secret funds, precious jewels, or even…" He laughed as his grin spread across his entire face. "Embarrassing photos from his chubby phase! Oh, I hope so."

John laughed too, and so did Mycroft. This was going to be most interesting.

Mycroft took the day off so he could keep watching Sherlock struggle with the box. By the time the skeleton key was ready, Sherlock had already discovered the false bottom and a few of the secret compartments, though of course he'd found nothing in them. Admirably enough, this didn't discourage him but only made him more determined. Mycroft might have felt sorry for him if it wasn't so funny. Oh Lord, was he going to be disappointed.

When a member of the homeless network brought Sherlock the key, he grabbed it and wasted no time in rushing toward the box with a devilish smile on his face. Mycroft inched closer to his screen. Wait for it…

Sherlock turned the key to the right. It didn't move. He tried turning it to the left. It gave a little, but not enough to open the box. He took the key out and turned it upside down. For ten minutes he struggled and grunted and Mycroft nearly choked on his popcorn watching his frustration grow and grow until finally he sat back and chucked the key across the flat, swearing at it.

"Jesus," John said, coming out of the kitchen. "So the skeleton key didn't work then?"

"Obviously," Sherlock said sullenly, glaring at the box.

"What's all this shouting about?" Mrs. Hudson asked from the doorway. "What are you boys doing?"

"Oh nothing, just Sherlock stole a top-secret item from the British government," John said.

Sherlock scowled. "Whatever Mycroft's got in here, he has no right to keep it from me."

"That box is Mycroft's?" Mrs. Hudson asked, pointing to it. When John nodded, she said, "Oh Sherlock, you shouldn't be breaking into his things. What if it's something private, like a journal?"

"All the more reason to get inside then!" Sherlock said. "He's always trying to spy on me, why shouldn't I spy on him for a change?"

It's for your own good, Mycroft thought as he checked the time. Twenty-six minutes. He muted the volume on his camera feed, then called Sherlock, reminding himself to sound furious.

The call went to voicemail. "Sherlock, I know you have it," Mycroft said, forcing himself to keep his voice hard and tight. "Give it back to me now, or I will be forced to take it from you by any means necessary. You have until one hour to return the box to me, or I will send in reinforcements." He hung up, thinking it best to keep the message short and sweet. He hoped Sherlock would figure it out before then. Sending in national security would be quite the waste of resources, but he had to make good on his threat or Sherlock would get suspicious.

Turning back to his cameras, Mycroft saw that Sherlock had listened to his message and tossed his phone away as he continued searching the box with his eyes. Mrs. Hudson had left, and John was standing there watching.

"There's another way to open it, there has to be," Sherlock insisted, turning it over and over in his hands.

Oh, there is, Mycroft thought smugly. Come now Sherlock, surely you can figure it out.

"Maybe it's voice activated?" John suggested. "That would be a good way of making sure only Mycroft could open it."

Mycroft nodded. That actually wasn't a bad idea; John was smarter than people gave him credit for. He made a mental note to file the thought away for future use.

Sherlock, however, shook his head. "No, he would need to entrust it to someone in case something happened to him. Or what if he lost his voice? There must be something else, something I'm missing…" He flipped the box over and stared hard at the bottom of it—the real bottom—and John tapped on it, remarking that it still sounded hollow to him.

Sherlock's face lit up like a light and Mycroft knew he had solved it. "As I said before, John, you are an excellent conductor of light," he said, and pressed on the entrances for all of the secret compartments at once. The lock sprang open.

Mycroft sat up and leaned into the screen. Oh, this was going to be good. Sherlock cheered and didn't bother to hide his greedy expression as he reached for the lid. Even John was clearly invested as he watched with interest. Sherlock's thin white hands took hold of the lid and pushed it up.

He yelled and cursed to the high heavens as John winced and covered his ears. Mycroft fell onto his side, laughing until his eyes nearly danced with tears as he watched Sherlock come to terms with what he had found.

For underneath the lock that required a key, there was another lock that required a combination.

"Your brother really doesn't take any chances, does he?" John laughed as Sherlock gave the combination lock a look that could kill.

"Shut up, John," Sherlock growled. "I need to figure out his password."

"Good luck with that," John said, getting up to leave. "I highly doubt someone like him would pick something you could guess."

Mycroft lay back on his bed again. He had invested in a lock with both numbers and lowercase and uppercase letters to make it even trickier. Unfortunately for poor Sherlock, he doubted his little brother would guess that the passcode only involved numbers. In fact, they were random numbers. He had discovered an app that shuffled numbers like a slot machine and gave you a random combination, and he had picked the first one it gave him. The goldfish of society thought they were being oh-so-clever choosing names and birthdays when those were the easiest passwords to guess. If you really wanted to fool a would-be hacker, you had to use numbers. The more numbers, the better your chances. Something Sherlock probably knew but would still ignore, since he always insisted things be clever.

He watched as Sherlock tried the easy guesses first. Different variations of names, addresses, their ages, the birthdays of everyone in their family, previous code names of missions, British sayings. Mycroft was amused when he even tried the word "umbrella" a few times and slightly annoyed when he tried "cake." When none of those worked, he tried years that had been significant, famous number combinations, and even Mycroft's clothing sizes. Finally he threw up his hands.

"Nothing! Nothing works!" He sent his fingers rustling through his curls furiously. "I don't understand, what else could it be?"

There was an echoing sound of heavy footsteps as John returned from his bedroom. "If he had wanted you to know what was in there, he wouldn't have guarded it so heavily."

"The bloody Bank of England isn't this hard to get into!" Sherlock said, slamming a fist onto the box. "Dear God, whatever's inside must be damn important."

John laid a hand on his shoulder. "All right, easy. Why not take a break, hmm? Maybe come back to it later? Can't think rationally when you're angry."

Oh no. Sherlock looked like he was halfway considering what John had said. Well, we couldn't have that, could we? Mycroft reached for his phone and dialed Sherlock's number. This time he answered.

"What do you want?" He sounded even angrier than he had on the camera.

"You know exactly what I want, and I am heading over to Baker Street right now to reclaim it." Mycroft pressed the button in his bedroom that would summon a car and began to gather his wallet and umbrella.

"Well you're too late, I've already seen what's inside," Sherlock said in a fake-smug voice.

"No you haven't," Mycroft said, biting back a laugh. "If you had, you would not be sounding smug. Why not make this easier on both of us and just hand it over?" When Sherlock didn't answer, he piled on the pressure. "Come now, Sherlock. You couldn't handle what I keep in that box. Now give it to me before you get yourself into more trouble."

Sherlock snarled. "Come take it from me then if you're so sure you can." He hung up, and Mycroft hurried out to meet his car, switching the camera feed from his laptop to his phone so he could keep watching this little spectacle on the way to Baker Street.

By now Sherlock had abandoned all pretense of cleverness and was prying away at the box with a crowbar. John, who as always had been roped into helping him, was holding the box in place and complaining about it. Mycroft was trying so hard not to crack up that more than once his driver had turned around and given him puzzled looks. As for Mycroft himself, his sides were hurting and his cheeks were killing him. He had laughed more today than he had in probably a decade. But it was worth it to see the frustration and panic on Sherlock's face, and to know it came from Sherlock doing the exact opposite of what Mycroft had told him to do. Perhaps once he learned the truth, he would also learn a lesson.

"Sherlock, it's hopeless!" John insisted. "I'm telling you, it can't be done. I'm pretty sure Jim Moriarty couldn't break into this bloody box."

"Shut up," Sherlock snapped again. He gave another yank on the crowbar between words. "He's not going to lord his precious little secret over my head. I'm—going—to—get—this—open—if—it's—the—last—thing—I—do. Dammit!" he tugged so hard that he collapsed backwards and his crowbar snapped in half. Mycroft thought with a wry smile that the box was going to be ruined by the time his brother was through with it, but that was all right. Every penny he had spent on that box was going to be well worth it.

As the car cleared the London streets and 221B was in sight, Sherlock switched from the crowbar to banging on the lock with a hammer to try and break it. Sweat was dampening his shirt and he looked so frazzled that Mycroft almost felt sorry for him. He might have felt remorseful if it wasn't all so funny.

The car stopped and Mycroft emerged. At his nod, the driver beeped the horn. The last thing Mycroft heard before turning off the camera feed was, "He's here, but there's one more thing I can do. There's one force that's stronger than any lock." Mycroft had a feeling he knew what that was, and he had just put his phone away when he heard the bang at the bottom of the stairs and the rushing footsteps that told him he was right. He opened the front door of Sherlock's flat to find him bending over where the box had landed at the bottom of the stairwell. It had finally smashed in two with both lids on the other side of the hall. Sherlock gripped the box and finally, with an almost cartoonish smile, looked inside.

"Sorry Pandora, but I'm afraid your search is over," Mycroft said, and he didn't bother to hide the delight on his face as Sherlock's smile dropped. John and Mrs. Hudson hurried out of their flats to see what was going on, and John snuck a peek over Sherlock's shoulder.

"There's nothing in it," John announced. "See? Told you it felt empty."

"It must be in one of the compartments," Sherlock said breathlessly. He stuck his hands inside the box, feeling all around its walls. Mycroft twirled his umbrella in his hands and watched.

It was John who noticed. "You're surprisingly calm about the fact that your brother just destroyed your top-secret box."

"And what can we deduce from that?" Mycroft said with glee.

Sherlock looked up and scowled, dropping the box on the floor. "Of course. You removed whatever it was because you anticipated that I would steal it."

"Well, you did steal it," Mrs. Hudson pointed out.

Mycroft could see he was going to have to walk Sherlock through this. "You might recall that our recent meeting in our office was the first time the box had ever been there. This was, of course, shortly after our last encounter where you made things difficult for me by yet again not listening to what I told you not to do."

"Yes, so? What's your point?"

Mycroft looked up. He was going to soak this up while he still could. In fact, he was going to document every moment in his own mind palace so that he could remember it whenever Sherlock irritated him again. "I drew attention to the box. I warned you repeatedly not to concern yourself with the box. Yet there is nothing in it. What might we deduce from that?"

All three of them were silent for a moment as the cogs turned in their heads. Then John and Mrs. Hudson began to smile. Sherlock was still thinking, looking at them bewilderedly, but his friend and landlady exchanged looks and giggled.

"I assume the two of you have figured it out?" Mycroft pointed to them.

"There was never a damn thing in that box, was there?" John asked with a smile. "You made him think there was just to mess with him."

Sherlock's face went from puzzled to livid.

"Oh now, that wasn't very nice," Mrs. Hudson said, although she was biting back a laugh too.

Mycroft gathered up what remained of the box. "I had this specially made specifically for the purpose of teaching my brother what happens when he makes up his mind to do the opposite of whatever I ask him to do."

"No," Sherlock said, shaking his head. "No no no, this is a trick."

"Yes, I believe we just made that clear. Pay attention."

"No," Sherlock said louder. He pointed to Mycroft. "This, right here and now, is a trick. You want me to think there's nothing so I'll stop trying. But there is something."

Mycroft didn't even know what to say to that. He shrugged. "I suppose if you want to continue your fruitless little search, I won't stop you. But I assure you there was never anything in the box." When Sherlock looked suspicious, Mycroft pointed to his face. "Look at me, Sherlock. Do I exhibit any of the physical giveaways of lying when I say that the entire matter was a ruse to trick you into making a fool of yourself?"

Sherlock stared at him for a good minute, scanning him with his eyes. Finally he turned on his heels, stomped up the stairs, and slammed the door of his flat so hard it shook the building. Mrs. Hudson winced and murmured "Oh dear" as she disappeared back into 221A.

"My apologies for the massive sulk he's surely going to have," Mycroft said.

John winced and nodded. "Was actually a clever joke, that. Not sure he'll ever forgive you for it though."

"That's perfectly all right, so long as he's learned his lesson," Mycroft said, and he walked out of Baker Street with a spring in his step he'd not enjoyed since the early days of childhood.