A/N: Inspired by a Halloween prompt from penaltywaltz. I'd post the prompt but that would give away the plot. Takes place the 2nd Halloween after Sherrinford.
I hate Halloween, Sally Donovan thought as she put another drunk and disorderly (this one dressed as It) in the back of the car. Scratch that, I hate working the weekend before Halloween. Everyone's on their worst behavior and guess who gets to clean up the mess. And we still have three more days of this shit.
She was working on her paperwork when Greg stopped at her desk. "I'm heading out," he said, "I'll see you at the Watsons'?"
Her mind blanked on why they'd be going to John and Mary's tonight. She didn't want to look completely out of it in front of her boss so she smiled a bit. "Yeah, soon as I'm done with this."
Greg grinned. "Don't forget the rule." He waved goodbye as he left.
Rule? The hell? She thought about calling Mycroft but rejected that idea. If I told him I forgot a social event, he'd never let me live it down. Guess I'll just have to wing it.
Sally and Mycroft had been "friends with benefits," as she put it, for the past six months. During that time, he had convinced her to swallow her pride and apologize to Sherlock for doubting him. Despite how she acted sometimes, she was very grateful that Sherlock had accepted her apology and that all of them now considered her a friend. Even Sherlock, albeit grudgingly.
None of them knew of her relationship with Mycroft, though. Sally knew they wouldn't understand. She barely understood it herself sometimes. They'd seek each other out when they needed a release or just someone to talk to. It usually amounted to a long, passionate weekend at his mansion then days or even weeks without seeing each other at all, just the occasional text or call to make sure the other was still breathing. There were many times that she wanted to see him in the middle of the week, just to spend time with him. He really was the smartest, most cultured man she'd ever met. What surprised her was that underneath all those bespoke layers, he had the heart of a romantic and the soul of someone born a century too late. Lately, she'd been daydreaming about waking up to him every morning.
Not that he'd ever agree to that, she thought as she filed her last report. Domesticity's just not his thing.
She finally left work an hour late and checked her email on her phone as she walked to her car. Nothing about a get-together. Either I deleted it or it wasn't emailed to me. No help from Facebook or Twitter either. Ugh…
Sally racked her brain the entire trip to Watsons' but nothing came to her. The note on the door told her to go on in. Taking a deep breath to prepare her for whatever lay ahead, she opened the door and walked in, groaning quietly as realization hit her.
Black and orange crepe paper streamers decorated the doorway to the sitting room and through it, she could see that more streamers and balloons suspended from the ceiling. "Monster Mash" was blasting and everyone was dressed up in some sort of costume.
Bugger… Should've known it'd be a Halloween party. No one's noticed me yet, I could just run home and-
Her thoughts were cut off by the host catching her eye. John looked her over as he approached her, raising an eyebrow. He was dressed as a zombie, complete with tattered clothes and some rather impressive make-up to make him look undead, though Sally suspected that the blood-shot eyes were due more to being a parent of a two-year-old and a newborn. "Hi, Sally. You knew a costume was required, right?"
She was about to say she forgot it was a costume party when Sherlock, who was dressed as Frankenstein's monster, piped up. "Obviously, she came as my brother. Same shirt and vest. Thankfully, her trousers are a lot more flattering. Considering the labels he prefers, that's still a great deal of money to spend on one night's attire." He smirked. "I do believe Sgt. Donovan wins for Scariest Costume."
Might as well go with it. She put on her best Mycroft smirk. "As always, little brother, you see but you do not observe." She showed him the cuffs and collar of the shirt. "These are not new, nor were they bought second-hand."
John stared at her. "You went to Mycroft's house and stole his clothes?" He looked equally impressed and scared shitless.
Mary came over, grinning. She was dressed like a zombie hunter, complete with fake crossbow and blood-splattered clothes. "Need a place to hide when the Iceman finds out? The girls would love to have a roommate."
Sally grinned back. "He won't find out, Mycroft doesn't do parties."
Sherlock raised an eyebrow. "Then who's that in the corner?"
She looked over and winced. Bloody hell...
Mycroft was indeed leaning against the wall in the darkened corner, his arms crossed in front of his chest. He was wearing last year's tuxedo, its looseness a testament to their frequent and vigorous activities.
Still, he looks damn good in it, she thought approvingly.
A black opera cape with a red lining completed the look. He wasn't wearing any make-up, but when Anderson, who was dressed as a Smurf, got a little too close, Mycroft hissed at him, baring a realistic set of fangs. Anderson quickly scuttled away. Sally was happy to see her ex having enough sense to leave Mycroft alone.
Mycroft caught her eye, one elegant eyebrow raised as he took in her attire. She gave him her haughtiest look then turned back to her friends and proceeded to deduce each of them. It was surprisingly easy, thanks to all the time she'd spent around the Holmes brothers. She could sense Mycroft's gaze on her the entire time and it made her feel warm all over.
Everyone was amazed at how good her Mycroft impression was. John called it uncanny and Mary suggested that she go into acting. When it came time for her to deduce Molly, who was dressed as the Bride of Frankenstein to match her husband, Sally realized that she was pregnant. Not wanting to pull a Sherlock, she instead mentioned the couple's new puppy.
"An Irish setter, going by the hairs on your sleeve." She grinned. "He's a handful already."
Sherlock smiled proudly. "That he is. We named him Hamish."
John rolled his eyes.
"Do Mycroft," Molly said, grinning.
Already am, Sally thought. "I don't know…"
"Oh, go on. We're dying to know."
Fortifying herself with a sip of spiked punch, she approached her secret lover with a grin and it widened when he smirked at her. "Your tuxedo is of the highest quality, so obviously not a rental. It's a size too large, but it fit you when you bought it a year ago. Down a size in a year, most impressive for a man who spends most of his time behind a desk. What would cause such a significant weight loss? Certainly not jogging, that never interests you for long." She grinned wickedly. "No, this is something else. Something exciting, engaging, and frequent. You, Mycroft Holmes, have a girlfriend."
She heard her friends burst out laughing at the thought, except Sherlock. Sally could only imagine how much he was deducing on his own.
Mycroft, for his part, never took his eyes off her. His gaze spoke volumes. "You are quite right, 'Mycroft,' I am seeing someone. A woman who knows me better than I know myself. A woman who has been running through my head constantly as of late." He smirked. "Are you getting tired yet, Sally?"
Everyone stared at Mycroft but only Sally's jaw dropped. He chuckled as he pulled her close and proceeded to snog her breathless in front of everyone. When they both needed air, he then moved his lips to her ear, murmuring, "Happy Halloween, my love."