A/N: Inspired by a Warstan prompt from afteriwake: "You stole my bra?" "It's not what you think." Post-S4 AU - Mary didn't die.
"You stole my bra?" Mary Watson asked from the doorway. She'd just caught her husband of two years trying to stuff one of her old and faded bras back in the drawer with the rest.
John quickly turned around to face her, his expression telegraphing his guilt loud and clear. "It's not what you think."
Mary raised an eyebrow, trying hard to not let her amusement show. "How do you know what I'm thinking?"
He nervously fiddled with his wedding ring. "Er … I assume you think I stole it because I want to wear it."
The retired assassin rolled her eyes. "No. If you wanted to wear a bra, I have much prettier ones."
"Um, you think I stole it so I'd have something of yours when I was, um, thinking about you?"
Seeing her fortysomething husband blush never failed to make Mary smile. "You never needed something of mine before."
"How do you- Never mind, I don't want to know."
Her smile widened. "Keep guessing."
"You think Sherlock wanted it for an experiment."
"Bingo. So, what poor woman died with that kind of bra on?"
John smiled a bit as he came over and wrapped his arms around her waist. "Actually, I wanted it so I would know what kind to buy you since that one's a bit worn out."
She wrapped her arms around his neck, smiling patiently. "John … that's my maternity bra."
"I know. Sherlock informed me this morning that you'll need a new one soon."
Her eyes widened. "How did he- Never mind, I don't want to know."
"Are you … happy?" John asked cautiously.
She grinned at him. "About having another baby? I'm thrilled. About Sherlock knowing first, again? No, but then I know something he doesn't know yet."
"What's that?"
"Molly's going to need one too."