It's miserably hot and muggy out, John is tired of chasing after Sherlock, and greatly looking forward to getting home, turning on the fans, and having a cold beer. They throw themselves into a taxicab and Sherlock's immediately pestering him.
"Can I use your phone? I want to send a text, but I don't want to use mine."
"Sherlock, I told you already. My phone is dead, I'll have to charge it when we get home. Use yours or be patient." John grins mischievously, knowing neither of those options is going to appeal to Sherlock, who just grunts irritably.
The cab pulls up outside 221 Baker Street and Sherlock lunges out, leaving John to pay and follow him up the stairs. He's been inside for less than thirty seconds and already Sherlock's got two laptops booted up in front of him, the telly on with the evening news blaring, and John's mobile charging. John didn't even feel Sherlock slip it out of his pocket, but he shrugs resignedly as he heads into the kitchen to grab his desperately needed cold beer.
"One day you're going to regret being so plugged in, Sherlock."
Suddenly, as if in response to John's prediction, the flat goes dark. The unwelcome sound of electronic devices winding down surrounds them as they plunge into a city-wide blackout.
Poor boys! Want to know what happens next (hint - it's sex)? Check out the fic "Blackout" on my AO3 account.