The Fat One
Mycroft looked at himself in the mirror. He sighed and smiled slightly at his PA. "If I had known that all it took was doing a little legwork, being infected by parasites, and suffering in the Brazilian jungle for seven months, then I would have gladly gotten fat."
She smirked and shook her head. "Just keep the reward, sir. Imagine how your brother is going to react?"
Mycroft couldn't help it, he laughed. He looked at himself in the mirror again and then sighed. "Unfortunately, all my suits will have to altered."
"Already being done, sir."
Mycroft nodded and then smiled wider, already looking forward to the reactions of his fellows. He straightened the suit that he had Anthea swipe from Sherlock's wardrobe, picked up his briefcase, and left the house. Anthea followed closely behind him.
Mycroft grinned mercilessly when he noted how one secretary ran into an actual wall, because she was too busy staring at him. Nodding to his colleagues, Mycroft entered his office and closed the door.
He was immersing himself in the treaty between Bolivia and Columbia when Sherlock burst into his office.
"Mycroft! Where have you been?! Mummy has been bothering me for months! Asking me where you were! If you were still-"
Sherlock stared at Mycroft as his older brother stood up.
"…alive."
Mycroft smiled smugly. "Apologies for resorting to borrowing one of your suits, Sherlock, but none of my old ones would fit me without being altered first." Mycroft huffed and then chuckled. "I'm afraid they'll have to be altered soon. Your shoulders aren't as wide as mine."
Sherlock looked his brother up and down and then let out a scream of frustration. "NOW WE LOOK LIKE BROTHERS!" He glared at Mycroft. "I'm going to get you fat again, if it's the last bloody thing I do!"
"What flowers would you like to have at your funeral?"
Sherlock stopped and then blinked in surprise. Mycroft smiled pleasantly. "I think you would be murdered by at least the secretaries, not to mention Mummy, and a few of the other officials in Whitehall." Mycroft straightened 'his' suit jacket and looked down at himself with pride. "Many have made comments about my improvement."
Sherlock shook his head and then groaned, putting his head in his hands despondently. Mycroft grinned. "Ah…tut tut, Sherlock. Don't look so glum. After all, we could always swap places. You could become the fat one."
The grin on Mycroft's face widened when Sherlock fled the office shouting at the top of his lungs.