Three years ago, the Phantomhive twins made a vow over a pair of graves:

Trust no one.

Never forget.

Show no mercy.

1. Trust No One—but each other.

The sea of heads bobbed and shifted under tree-dappled sunlight, but Robin Phantomhive could spot her twin brother from the school steps. He was the only other person she knew with the same hair as hers—an exotic blue-black shade. The only other living person, that is. In an attempt to be heard over the schoolyard clatter and urban traffic beyond, Robin cupped her hands around her mouth and shouted "Hey bro!" Before darting off through the mob of children to her twin.

"Hey 'Sis'," Ciel Phantomhive greeted dubiously as his twin slung her arm through his.

"Wanna go to Angelique?" Robin asked, tilting her head so that one curled pigtail brushed the ruffled black hem of her blouse, "we can compare notes."

Ciel remained silent and shrugged, but turned left toward the Bleecker Street rather than right towards their Soho apartment. Robin smiled, happy to have gotten her way.

The thirteen-year-olds walked into Cafe Angelique, still arm-in-arm. They were regulars, showing up at the cafe almost every day, either in the morning for complicated espresso drinks and fruit-filled Belgian waffles or the evening for fancy quiches and frozen mint lemonade. Ciel and Robin had earned the moniker "Hansel and Gretel" from the usually-blase waitstaff, all of whom doted on the young twins.

"You two look darling!" The thirty-something behind the counter declared, referring specifically to their crisp new, incidentally matching school uniforms.

"Thanks," the pair replied in unison, Ciel flatly and Robin with more enthusiasm. While her brother absently tugged at the hem of his red plaid vest, Robin executed a small curtsy, flouncing her identically patterned skirt.

"What'll it be?" The woman smiled, amused.

"A Strawberry Alarm Clock," Robin said grinning while Ciel considered the cupcake display and proclaimed, "one A Clockwork Orange." An instant later they simultaneously added, "and an iced Earl Grey."

On the way to their usual table, the twins raised their brows at each other; Ciel said, "I wonder what Freud has to say about clocks," and Robin giggled.

Cafe Angelique was a favorite place for the twins; when they were young, their parents would take them here every Sunday after church. It was a timeless sort of place, all exposed brick, delicate wrought iron chairs, and little orange bistro tables. The waitstaff left the customers alone for the most part, and the cathedral-like acoustics encouraged diners to talk in murmurs. Ciel and Robin appreciated the privacy.

Their favorite table was against the near wall, just before the window. The cafe was barely lit during the day, and the natural light that seeped in was just enough to read or write in. Perfect. After their elaborate cupcakes arrived, the twin's finally started talking about their first day of 8th grade.

"I almost forgot how idiotic other children were," Ciel spoke first, neatly bisecting his confection to reveal matching pockets of orange mousse set deep in citrus cake.

"Just the children?" Robin widened her bright cerulean eyes, "What are your teachers like?"

Ciel leaned his elbows on the table as he fastidiously scooped mousse from cupcake's center. At his sister's comment, the boy looked up from the gutting-process and smirked. "Sometimes, I think we're the only two sensible people on the planet."

With a satisfied little laugh, Robin swirled a finger around her confection's pale pink summit of icing. "The only two that matter, anyway." With a smirk that rivaled her brother's own, Robin popped the finger into her mouth and reveled in the saccharine strawberry taste.

Sitting there, straight across from the other with matching smirks on matching cupid's bow lips, and matching cruel gleams in their matching cobalt eyes, the Phantomhive twins may as well have been looking into a mirror.

2. Never Forget—the pain they've suffered

The world was white and red and searing heat and ear-popping noise. It's like a firework, Robin's shock-dazzled mind thought, and then she was screaming because her parents were in that firework and the car was still on fire, and there was nothing but a car-shaped inferno, dancing before her eyes. She was on the ground, a few feet from Ciel who'd been blown back along with her when the explosion hit, and everything hurt.

Eyes blind and stinging from smoke and too-bright flashes, skin raw and prickly from the heat, ears aching from the noise, throat raw from screaming and screaming and—

For the hundredth time in the past three years, Robin woke at 2 am with heavy sobs choking her throat. Sitting up in her overstuffed canopy bed, the thirteen-year-old knew that sleep was out of the question. She also knew that Ciel was awake, roused by the same dream as she.

Careful not to waken Mr. Tanaka—their very-elderly-but-very-kind guardian—Robin tiptoed passed her brother's room and down the hall. The office had been their father's, a mysterious room to which access was forbidden. As children, the twin's learned to pick the lock and sneak into the office, but none of the papers made any sense to them, so they stopped risking it. It was their office now, and they knew what it was for.

Now Ciel sat at the desk in a chair far too big for him, pallid in the harsh blue computer screen glow. Just behind him, an enormous armored glass window looked out upon darkened art galleries and boutiques, neat-but-lonely streets where the occasional couple or barefooted girl straggled home from a night out in Greenwich Village.

"Spread sheets?" Robin queried. When Vincent Phantomhive died, he left behind two family businesses—one legal and one less so.

Ciel could not have heard her approach, but he showed no surprise at her presence. "Figured I'd get a jump on next quarter."

"You worked out last quarter's profits already?" As Robin made her way over to the desk, the pink satin ruffle that capped off her nightgown swished pleasantly over her knobbly knees.

"Yesterday."

"Do you have the papers? I'll check your math," Robin offered. The numbers were tricky on the final papers, and both twins always looked it over.

"My math is perfect," Ciel replied archly.

"Then you certainly won't mind me checking it over," Robin retorted, not missing a beat. She and Ciel were both proper geniuses in their own rights, and extremely arrogant about it.

Grudgingly, Ciel opened a drawer and handed the pristine sheath of papers to his sister. In return, Robin gave him a sugary smile and dug into the bottom drawer where Ciel stashed his sweets—the good stuff, from Dylan's Candy Bar.

With her stack of papers and a dime baggie of chocolate-covered gummy bears, Robin curled up on the upholstered loveseat that still smelled like her father's cologne. The scent dredged up memories of bedtime stories that went on till midnight, of tramping through unexplored city streets with Sebastian—a golden retriever they'd found in Washington Square Park and raised in secret. The truth was, Vincent Phantomhive was not a very good person, but he'd been a very good father. That was what Ciel and Robin remembered, and that was what mattered. They would have revenge for their parents' deaths; it was just a matter of planning and patience.

After all, the Phantomhive children were supposed to die in that car bomb explosion three years ago as well, and who could stand leaving a job like that unfinished?

There were many nights like this, when the twins would huddle up in the office with mundane piles of paperwork, or on the leather couch in the den, watching cop shows and Masterpiece Mystery reruns. They would grumble over misplaced decimals in number columns or try to outsmart each other by guessing the criminal and murder method in the program. Hounded by dreams that were actually memories, the twins tried to escape the past without allowing themselves to forget.

3. Show No Mercy—to those that had wronged them

The face that gazed back at Robin from her white rococo vanity set was bored—a girl trapped behind a pane of glass with nothing to do but watch her reflection drag a brush through her long, blue-black hair again, and again, and again...

Wait

Robin jolted up, as though shaken from a deep sleep.

Something's happening.

The girl hopped off her stool and flitted down the old spiral staircase, hopping from the final step onto the first floor of the apartment. There were voices in the kitchen, Ciel and someone unfamiliar. This was curious because Robin would have heard anybody come in the front door, which meant they used the side door. Well, Robin could count on one hand the people who even knew there was a side door—herself and Ciel included—and only a few of those had access to a key that opened the door, which meant...

Robin gave a disbelieving little laugh before slipping into the kitchen to find her brother and a dark-haired man with disconcerting red eyes. Yes, she remembered this one: Sebastian "The Crow" Michaelis, a mercenary they'd hired. At his side was another man, an unconscious one with his wrists and ankles bound. It was like Christmas.

"There's the matter of payment..." Sebastian was saying, and Ciel was nodding.

"Help me with this," the blue-eyed boy nodded at the refrigerator, and Robin had to muffle a laugh. Ciel was exactly her height, but he was tiny compared to a tall man like Sebastian. The funny thing about it was that you'd never guess it from the way he acted, and Robin supposed she was the same.

When the fridge was cleared Ciel strode over to the newly exposed safe, shielded the keypad with one hand, and entered the pass code in with the other (1-0-6-0-6, not that Robin was about to say it out loud.) Sebastian gave a low whistle as Ciel stepped into the vault, then emerged with a wad of high-marked bills. He handed them off and Robin chose that moment to make her presence known.

"So who's our guest?"

Two male gazes shot to her, one devoid of emotion and one filled with concern. It was the mercenary that was concerned. "Ms. Phantomhive, maybe you should go back upstairs."

"Why?" Robin said defiantly, cocking a brow.

"To be blunt, this isn't a matter for young girls."

"I'm the lady of this house," Robin declared, boldly with an edge of challenge.

Sebastian almost seemed amused. "The very young lady."

By this point, Ciel was rolling his eyes. "Enough. She's my sister. Of course she should be here."

"Thanks, Bro," Robin replied with an identical eye-roll as her ballet flats hissed over the tiled floor.

Sebastian merely shrugged and proceeded to tie the unconscious man to a chair at Ciel's instruction and drag said chair into the safe. Idly, Robin pulled a kitchen knife from the holder on the butcher block and ran a finger over the blunt end. "How long till our friend wakes up?" she wondered.

"I recommend icy water," Sebastian replied helpfully. Robin nodded and filled a cup from the sink, deciding that somewhat cool water might do in a pinch.

Glass in hand, Robin went to stand beside her twin at the mouth of the safe. The briefest of grins flashed between them before Ciel looked over his shoulder at Sebastian. "Wait there...help yourself to whatever's in the fridge."

"I kinda like him," Robin murmured.

"He's a good dog," Ciel agreed. "Ready?"

By way of response Robin flashed a brilliant grin and tossed the contents of her glass over the bound man's head, then the glass itself. "Rise and shine!"

"Wh—uh" The captive blinked up, eyes gaping blindly in the semi-darkness.

"Hello, my name is Ciel Phantomhive," Ciel said evenly, "I believe you know a thing or two about my parents' murder."

Murky green eyes adjusted to the dimness and took in the small figure standing before him. An ugly laugh bounced off the metal walls, and Robin almost winced. "You're just a kid!"

"Brilliant observation," Robin interjected icily, swiping the pilfered knife in an unpracticed slash across the man's face, pleased to hear him scream.

"Any other deductions?" Ciel finished, watching the cut open and ooze red.

In the end, they left him in the safe for a few days. He choked up a name when they finally opened it, and then Ciel put a bullet through his head. After all, they'd made a pact over their parents' graves, he and Robin—no mercy.