spectralarchers on tumblr said: I want a Cabinlock fic where Martin and Theresa are on a double date with Sherlock and Molly.
So this is my response. Background Sherlolly, foreground Martin x Theresa. Enjoy!
"Whose stupid idea was this?" Martin hissed in an aside to his gorgeous, wonderful, perfect fiancée. They were dancing, something slow and lovely and normally all he'd be able to think about was how well they fit together when they danced, but today…today all he could do was watch his stupid cousin dancing with HIS fiancée, looking like he'd been a professional ballroom competitor in a previous life. Or possibly this one, between solving crimes and having arch-enemies and faking his death.
Theresa gave a soft laugh. "Yours, dear," she replied. "Remember? You said you wanted me to meet everyone in your family, even the annoying ones - and you have to admit, Simon was charming."
"Of course he was," Martin grumped. "Everyone in my family's been charming to you because they think you're perfect." He looked (slightly) up at her and smiled, knowing he looked goofy and not even caring. "Which you are."
At that moment his stupid cousin said something in a low voice, causing his dance partner to let out a cute little giggle-snort, and his attention was back on his grievances. The only thing that could make this worse was if Douglas was there, making snarky comments over his shoulder about his inferiority complex.
He glared daggers at his smug, overrated, too tall brainiac of a cousin William (he REFUSED to call the git 'Sherlock', stupid bloody show off couldn't even use his perfectly good, normal first name, who did he think he was, bloody Mycroft? Ugh, the even WORSE cousin who would be joining them at a family dinner next week, why why WHY did he do these things to himself…).
"Breathe, Martin," Theresa murmured, stroking soothing fingers down the back of his neck. "Remember, you're just as brilliant in your own way - and if you don't believe me, I'm sure Arthur would be more than happy to tell you so, next time you talk to him."
He wasn't normally one for PDA, but he couldn't help it; he leaned over and kissed Theresa full on the lips. She was right, as always; just because William was taller and had never had any problem getting girlfriends and lived some bizarre sort of James Bondish life as a 'consulting detective' didn't mean he could fly a plane. Not even something easy like a Cessna 150, let alone a real challenge like GERTI. And, of course, there was the fact that he'd gotten engaged YEARS later than Martin had. Hah!
How William had managed to get a woman like Molly Hooper to not only fall in love with him but to agree to marry him was a mystery for the ages. Even Aunt Violet couldn't explain it - and Mycroft, well, he'd never even THINK of asking that pompous ass about it.
Ugh. Mycroft. Just the thought of the family dinner he'd be forced to endure with him and Simon at the same table was enough to give him the collywobbles. Unless…with a devious gleam in his eyes, he asked Theresa, "Do you think it would all right if I invited Douglas to that family dinner next week?"
Her delighted laughter was all the answer he needed.