Sherlock tends to have a certain kind of dedication when the situation is important enough for him. Inspired by the scene in The Great Game in which John calls him to be a photographer and Sherlock's immediate response is to drop everything and leave.
Mike finds it all very funny. John isn't entirely sure what "it all" is.
Secretive Humor
"John? Is anything wrong?"
"Why do you automatically assume something's wrong?"
"You need an umbrella, don't you."
"...Yeah. You want to bring one over? I'm sorry, I know you're studying for midterms..."
"Think nothing of it." There were sounds of rustling and a door slamming. "I'm on my way. Be there in twenty. I'll walk home with you."
For some reason, this made John smile. "See you soon." He hung up and looked back to Mike at the counter. He was a bit embarrassed to find him grinning at him past a tumbler of mango tea.
"Something funny?"
"Oh, yes."
Prompt was #81: mango
Dad ate all my fancy foreign cheeses! D: *sadface* It cost me so much, too...I'm willing to share, but not if he plans on killing it. Argh.