There were strange smells coming from 221C. John would have to have a word with Mrs Hudson, because she'd either used too many chlorine-based cleaning agents to get rid of the black mould growing in the basement flat, or something else was amiss, and he didn't particularly want any potentially dangerous substances seeping through the floorboards of 221B. It was enough that Sherlock kept potentially dangerous substances in their kitchen which these days exploded with amazing regularity.
Coming back from work, John went into the living room, hanging up his coat and heading for the kitchen to make his customary cup of tea. Sherlock was studying something on the laptop – his own, for once – but before John could look over his shoulder to see what was so interesting, Sherlock had shut it down. “I need to go out, have to get some supplies for an experiment. No need to wait up for me”, he announced, grabbing his coat. He was gone before John could reply. He sighed. A quiet evening of mindless telly it was, then.
A few days later, John had what was possibly the busiest day at the surgery he'd ever experienced. He saw everything from a child with a toy soldier stuck up his nose to an elderly man with his eyes swollen shut from an allergic reaction, and barely had the time between patients to grab a cup of tea and have a bite or two of a sandwich. The only upside was the friendly hug he'd received from Sarah before diving back into his office. By the time his shift was over, he was exhausted. For once, he was glad that Sherlock had no case on. There had been no texts at all during the day, another thing he was grateful for. He made his way home without even paying attention, navigating public transport with the easy absent-mindedness of a London commuter.
By the time he got home, it was slowly growing dark outside, but there were no lights on in their flat. Sherlock was nowhere to be found. John flopped himself down on the sofa, rolling his head and shoulders to get the cricks and tension out, and finally closed his eyes. His mobile buzzed. He debated whether to ignore it, when it buzzed again. Resigned, he looked at the texts. Sherlock, of course.
“Get on the roof. - SH”, said the first text, and John frowned. What was going on? Even more confusing was the second text, which simply said, “Please. - SH”. He checked again – yes, the text was from Sherlock. Who wanted him to get on the roof of 221 Baker Street. Oh well, better get it over with, he thought, wearily unfolding himself from the sofa. He climbed up the stairs to the second floor, then up the ladder and through the hatch onto the little roof terrace. He looked around and his eyebrows rose involuntarily, because there was Sherlock, sitting on a picnic blanket, leaning back on one of the chimneys with cushions stuffed behind his back, gesturing for John to join him. “What...” John started to say, but Sherlock shushed him and produced a picnic hamper. He was clearly intending for them to have a picnic on the roof, and John found that he was actually quite hungry, so he shrugged away his arguments and settled himself next to Sherlock.
They ate in amiable companionship, chatting idly about their latest case and John's day at work. The story of the girl with the toy soldier up her nose made Sherlock chuckle into his wine, and by their second glass John was convinced that this had been a wonderful idea. Their meal finished, Sherlock grabbed a blanket and spread it across them to ward off the late evening chill, and they just sat for a while, watching the London skies and listening to the traffic noises drifting up from below.
John was feeling quite relaxed when he felt Sherlock reach for his mobile. He should have known better, he thought ruefully, Sherlock was probably getting quite bored by now, even though this had been his idea. But after typing out a quick text, he put the phone away again and resumed to look out at the sky. Smiling faintly, John closed his eyes, but opened them again with a snap when something nearby exploded.
And then he just sat silently, because instead of the bomb going off or the car backfiring, he saw fireworks. Green, sparkling silver, yellow, turquoise, all being let off from across the road, all in sight of their little picnic. Sherlock was speaking quietly now, explaining that the green was barium chloride, the orange calcium salts, the silver sparkle aluminium flakes, the yellow sodium chloride, and John understood. Sherlock had made these. This was where the strange smells from 221C had come from, this was what Sherlock had been experimenting on. He had made, from scratch, a fireworks display for John.
He turned to Sherlock, whose face was illuminated by the colourful display, whose eyes were sparkling with reflected fire, who was looking at him with a gentle, genuine smile. “Thank you”, John said, “this is... “ Words failed him, and all he could do was repeat, “Thank you.”
Sherlock reached out to lay an arm around John's shoulder, drawing him close. “Happy Birthday, John”, he whispered as they looked out across the sky to watch the dancing lights.