John didn't know what was happening until he checked his reflection in the glass case of the frozen foods aisle. Then he stifled a scream much louder than the one he gave in reaction to Sherlock's sudden otter-ness. Something excruciating was happening to him. His arms and legs felt like they were being liquefied, and then stabbed with red-hot needles all over. Suddenly, the shelves of ice cream rose way above his head, or—wait, no, he was shrinking. His clothes dwarfed him, and he struggled to emerge from the mass of jumper and trousers. Finally, all was still, and the pain of transformation disappeared.
John looked at himself through his small, beady eyes and panicked. Where was his sandy hair, his human-sized arms and legs? Why were his clothes in a pile beside him that seemed impossibly large in comparison to himself? And, were those...spikes on his back? He nearly fainted with recognition. He was a hedgehog.
Sherlock was forced to take a separate route back to the flat after his library visit, after he noticed cameras lurking on rooftops near his planned path. Unfortunately, the idiot shop owners would probably call the police if they saw an otter walking upright through London. Which was a shame, really, because seeing something like that would have made his day much more interesting.
Sherlock made the final dash towards the outside door to 221B, darting through a group of American tourist girls stupidly giggling about some man they'd seen. Then he heard a familiar voice behind him, but it sounded alarmingly different.
"John!" he exclaimed, pleased. Then he turned around, hushing himself. And looked at the hedgehog that was his flatmate. "Ah...I see. Well, where's the milk?"
"Sherlock?" said John, anger and disbelief choking his voice. "What the...are you serious?!"
"Look, John, it really isn't hard to buy things, even with your average mental capacity. I'm, frankly, surprised at you."
"I...am...a... hedgehog, Sherlock! My apologies if I didn't walk right up to the manager as a spiky little talking mammal and ask for milk for my insane otter flatmate!"
"Thank you," Sherlock said, appearing exceptionally annoyed. "Now, we should really get inside before a crowd forms."
A crowd already had. Some were clapping at what they believed to be very impressive special effects, others looked confused, and still others stood and stared. John and Sherlock hurriedly turned towards the flat door and John took out his key, but what they saw was not the gold lettering and knocker they expected. Instead, it was a blank, black door.
"What?!" cried John, his voice cracking in what was already a higher register than he was used to, being a hedgehog. "That's impossible! Sherlock, quick, try to push it open before─before an animal control unit gets here." They both shoved with all their might, but it was no use-the door was shut for good. Sherlock's brow furrowed. He was, as hard as it was to admit, completely lost-but he couldn't let John know that. Then, he got an idea.
"John—come on, we have to go find Moffat!" he said, determined.
"Who's Moffat?"
"A writer and producer of Sherlock…" he said disdainfully. "Unlike you, I did my research."
And without another word, Sherlock sprinted off into the night.
John himself prepared to get in a cab and catch up to his flatmate, but something else caught his eye. The crowd of people that had been surrounding them had not left, but instead shifted their focus to another man, standing nearby. John hopped over slowly to get a closer look, avoiding pricking people with his quills as he went. He edged his way into the circle of densely packed tourist feet, and got the important man's attention by stomping.
"Who—who are you?" he then squeaked cutely.
"Is it just me, or did the hedgehog just talk?" he said, pandering to the crowd. His "audience" laughed weakly. Then he shook his head in disbelief of the situation. "I'm Steven Moffat."
"Really?" said John happily, not believing his luck. "We need to talk to you!"
"We? You and what army?" Moffat replied.
"Me and Sherlock Holmes."