"They're totally shagging."
"What?!" John blurted out nearly spitting out his tea in the process. He stared incredulously at his wife.
"Sherlock and Molly. They're having sex." She replied. John could not believe what he was hearing. Mary who, until this moment, he believed to be totally sane, thought that Sherlock Holmes was shagging Molly Hooper. Sherlock Holmes! The self-proclaimed "high-functioning sociopath" getting it on with the woman who was head over heels for him, but whom Sherlock, as it seemed to John, almost completely ignored except when he needed something from her? No. There was no way this was happening.
While it was true that Sherlock had been much more friendly toward the pathologist since he had come back from the "dead", John didn't think the detective would ever be the type to have a girlfriend. Mary must have taken a dose of loony pills as far as John was concerned.
"I don't believe that for a second. What would make you think such a thing?" She must have been talking to Anderson again. That was why she was coming up with all these crazy notions about Sherlock and Molly. John went back to sipping his tea certain that whatever his wife was about to say would have no foundation in reality.
"Have you seen the way they look at each other?" So that's what she had to base her theory on? A few looks between friends? Her argument was not looking good. "And Sherlock is always spending time with Molly at Bart's nowadays."
"I haven't noticed him going any more than usual. And he only goes when she's on shift because no one else will work with him, and I don't blame them."
"What about last Tuesday?" She mentioned with a knowing smile on her face.
"Wait, what happened last Tuesday?"
"You didn't hear?" When John shook his head, she continued. "Sherlock didn't have any cases on at the time, yet he still went to the lab. He didn't do any experiments. He just talked to her for a while then he left. She told me that he even complimented her! And while she was telling me all this, she was blushing and fidgeting. She was hiding something! They are definitely having sex!"
"That's all you've got? Really?" Mary nodded with a triumphant look on her face, but John was still not convinced. "Just because he gives her a few looks, and tells her she looks nice doesn't mean they're shagging. That is not enough evidence. Sherlock Holmes himself wouldn't even come to that conclusion with so little information."
"Trust me. I know what I'm talking about." She replied still very sure of herself. "You just wait and see."
"Alright Mrs. Watson, whatever you say." He smiled as he grabbed her waist, and pulled her onto his lap. "Now, speaking of shagging…"
—-
A week later, John and Mary were in the lab with Molly and Sherlock. John was there because he and Sherlock were on a case, and Mary was there to "drop off Johns jacket because it's rather chilly out." It was a terrible excuse John thought, but she was intent on proving her point, and the only way to do it was to see both Molly and Sherlock in the same place.
Sherlock was working at his microscope, while Molly was filling out some paperwork. John and Mary were chatting, and just when John was about to tell his wife that she was wrong, and they were absolutely not together, Molly got up from where she was seated. When she walked past Sherlock she gave him a small smile, and to John's astonishment, he returned it. Still firmly believing that nothing was going on between them, he brushed it off as insignificant, but then wait- he wasn't- yes! Sherlock Holmes was checking out Molly's arse!
John absolutely could not believe what he was seeing, but there it was. Sherlock was ogling Molly's bum with a smirk on his face and a hungry glint in his eye. Mary saw the whole exchange as well and was looking at John with an "I told you so!" face.
"We'll its rather late, and I think John and I need to be heading home. Sherlock can manage without you dear, can't you Sherlock?" Mary said as she grabbed John's hand and started pulling him towards the lab doors.
"Yes, I think it is time for you to leave." Sherlock said while still looking over at Molly who squeaked in a "Goodbye!" before the Watsons were completely out of the door. The last thing they saw was Sherlock getting up off of his stool and making his way towards the pathologist.
John and Mary could not get out of there fast enough before the distinct sounds of giggling, and- oh god was that moaning?- could be heard on the other side of the door.
—-
Two years later, at the wedding of Sherlock Holmes and Molly Hooper, John and Mary were watching the newlyweds during their first dance. Mary leaned over to her husband and whispered "See, I was right all along."
"And I am so glad you were Mrs. Watson." John replied, turning his attention back to his best friend who was dancing with his new bride. Sherlock Holmes, the man who thought he didn't have a heart, only had eyes for the woman that proved he did.