Wars We Fought, Things We're Not

https://archiveofourown.org/works/328...

“Oh come, John. Could be fun,” Mycroft taunts, accompanied by an eyebrow arch he’s gotten far too good at. “Besides, it’s not as if it’s your first time pretending to be a couple.”

Five months after John's world has fallen apart, Mycroft sends the consulting detective and his doctor on a case that neither is prepared for.