"I'll only do it if you have protection, do you have any?" Molly frowned, she was eager to get on with this but she had a sneaking suspicion that 'protection' had been the last thing on Sherlock's mind when he asked her to join him at Baker Street that night.
Sherlock prowled toward her, but stopped dead in his tracks about two feet away. An intrusive and long ago repressed memory had chosen that exact - and highly inconvenient - moment to reassert itself.
ooOoo
25 years earlier:
Doctor Vernet Holmes sat his prepubescent son down at the kitchen table and drew a breath, "Son," he said, "you're old enough now that we need to have 'the talk'."
A 12 year old Sherlock squirmed in his seat. God, this was mortifying.
"When a young man," Vernet cleared his throat, "begins to experiment," his son winced at the word, "and especially when he does so with partners-"
"Partners?" Sherlock asked, suddenly curious, "you mean you can do it with more than one person at a time?"
"Well, yes," Vernet said, "your mother and I only experiment together now-"
"Daaaaddd," Sherlock whinged and face palmed himself.
"-but it's not uncommon to have several partners, men, women, sometimes several of either, together, and all at once." Vernet smiled wistfully, "Why I remember once - my very first semester in college mind you - doing it with 3 others, one of which was your Mother," he winked, "so fulfilling, so satisfying, as it always is when you're young-"
"Dad, is there actually a point to this humiliation, and will you be getting there soon?"
"Yes, well, my point being Son, that no matter who you experiment with, no matter how many others there are, be they men or women or where ever they fall on the vast spectrum of genders, it is always, ALWAYS, your responsibility to be accountable for your own health and well-being." He placed a firm hand on his son's shoulder, "Mother and I love you too much to be able to endure anything taking you away from us, so you must promise me you will remember to use protection every single time. No matter who it is, no matter how much you trust them, no matter how impromptu the experiment is, and most especially if you care about them - because you don't want them to suffer harm either Sherlock - promise me, my boy, you'll always be safe and use protection?"
If it would put an end to this frankly patronizing and ridiculous talk, young Sherlock was prepared to say anything. With his most angelic and innocent look he said convincingly, "Yes Father."
"Good lad," Vernet beamed at him with pride, "off you go now, your violin lesson starts in half an hour, you don't want to be late."
ooOoo
"Sherlock?" Molly snapped her fingers before his face, "Did you hear me, I asked if you had any protection or whether I should pop out to the chemist."
He stood there in his kitchen thinking about how his Father had schooled him years before, realizing that this was the exact moment he was talking about. He'd never once worried for his own safety - God knows he'd taken enough chances with his life over the years, he'd been reckless and rarely used protection - but he could never endanger Molly, who he loved so much. He was grateful now that some sensible part of himself that he usually kept well under lock and key had prepared for the moment when his experiments would no longer be solitary affairs.
"I do. Especially," he dug into his kitchen cabinet and produced two sets of safety goggles and a box of disposable lab gloves, "when it's for science and someone I love."
Sherlock kissed her nose and smiled as she accepted his offering.
"Come on then," Molly smiled, poking at the as yet unidentified substance Sherlock had brought home from the crime scene "let's see what the chemistry of this thing is then."
"Indeed," he pulled her close and kissed her, "I have a feeling the reaction is going to be volatile."