Mycroft tapped three times on the flat's inner door with the handle of his umbrella and waited three seconds before entering 221B.
He was greeted by the sight of Dr John Watson stood stock-still in the middle of the living room, holding a bucket above his head. His younger brother was cowering on John's armchair, his eyes wide with ill-disguised fear and his long, milky fingers running through his tousled hair nervously. Mrs Hudson was stood next to Sherlock, patting his shoulder in a comforting manner. All three of them were staring at the bottom of the sofa steadily. Nobody noticed his arrival.
Mycroft observed the scene for a few seconds then spoke up, "How did a frog get in here?"
John looked up and gave the eldest Holmes a warm smile, at which Sherlock barked at him to concentrate in an uncharacteristically high pitched voice. Mrs Hudson gave a little wave, but Sherlock didn't acknowledge his brother's presence. Mycroft smirked and closed the flat door behind him.
"I repeat, how did a frog get in?"
Mrs Hudson shook her head sadly and clutched one hand to her heart, "Oh, it's all my fault, Mycroft. I thought he'd like it, I never imagined-"
"Well you simply did not think; did you, Mrs Hudson?" Sherlock snapped, pushing himself further into the armchair.
John looked at Mycroft apologetically, not lowering the bucket.
"Mrs Hudson was babysitting her sister's grandson," John said by way of explanation, "And he'd brought his pet frog with him."
Mycroft tightened his lips to hold in a chuckle and glanced sideways at his sibling, who was glaring right back at him.
"And I brought him upstairs," Mrs Hudson said, "I thought that Sherlock would love to see little Trevor-"
Sherlock grumbled something that could have been "ridiculous name..." under his breath, and Mrs Hudson furrowed her eyebrows at him worriedly.
"Long story short," John continued, "Trevor made a break for freedom and is currently under the sofa, and none of us can reach him. It was only then that Sherlock's little ...problem came to the surface."
Sherlock sat up stiffly and gripped the arms of his chair angrily, "It is a perfectly reasonable phobia, John! Ranidaphobia is a widely acknowledged medical term- as a doctor you should know this better than anyone!"
John and Mycroft shared a look of exasperation.
"Look," Mycroft said, removing his coat and hanging his umbrella on the door handle, "I'm sure we can solve this painlessly, Sherlock. Where is the boy?"
"What boy?" Sherlock hissed.
Mycroft exhaled, unperturbed, and instead addressed John and Mrs Hudson, "The boy who owns the frog."
"Nathan? He's downstairs." Mrs Hudson said, looking at Sherlock cautiously.
John locked eyes with Mycroft, "Nathan was trying to help, but he" he tipped his head in Sherlock's direction, "made him cry."
Mycroft tutted and shook his head at the younger Holmes in a patronising manner, causing John to snigger.
Sherlock glowered at his brother over the top of the upturned collar of his coat, keeping his spindly legs folded underneath him, the toes of his expensive Italian shoes poking over the edge of the armchair. Despite his fury, he kept throwing wary glances at the sofa and recoiling slightly. He looked like a scared child. Mycroft was enjoying this more than he normally did, as this time there were other witnesses to Sherlock's humiliation.
"Oh Sherlock, I'm ever so sorry. If only I'd known you were scared of-" Mrs Hudson started, wringing her hands anxiously, but she was drowned out by Sherlock's cry of terror as he sprung up onto the back of the chair and thrust a shaking hand in the direction of the sofa.
"There it is!" He shrieked, "Now John- John get it now!"
John threw himself onto his belly and slammed the bucket onto the floor then curled around it as if he was fighting for possession of a rugby ball.
Sherlock visibly relaxed his muscles and slid fluidly back into the proper seated position, before tenting his fingers and looking directly at Mycroft as if he had not been curled up in a frightened ball just seconds before.
"So, what do you want?" he asked calmly.
Mycroft walked past the crouched forms of John and Mrs Hudson, who were ushering Trevor back into his carrying case, and stood next to the armchair.
"Just checking up on you, little brother." Mycroft said in a low voice, "My my, you really outdid yourself this time, didn't you?"
Sherlock folded his arms and faced the other way dismissively as Mycroft returned to collect his umbrella and coat.
"Right, now we've avoided that potential crisis, I'll make my leave."
John looked up curiously, "But you only just got here, don't you want a cup of tea or something?"
Mycroft smiled at the doctor, but it didn't quite reach his eyes. He never accepted John's offer of a cup of tea, but always appreciated the gesture.
"No thank you John, I really must be going."
He hung his umbrella over his arm, and nodded politely at each of 221 Baker Street's various residents, "Goodbye Mrs Hudson, John... Kermit."
Sherlock scrunched up his face angrily and his hands curled into fists as Mycroft left the flat.
"I don't know who he thinks he is, he has absolutely no respect for-"
"Do put a sock in it, Kermit." John said with a sigh.
Sherlock stared at John in betrayed shock for a few seconds before settling into a scowl, still keeping one wary eye on Trevor.