A/N: Okay, so I know I'm definitely supposed to be working on All I Ever Wanted, but I had plot bunnies about this one and I gravely apologise. I'm sorry. Also I've had atrocious writer's block for a month or so and this is the first thing that's stuck in my brain enough to let me write it. Again, I apologise.

Warning: People die in this fic. It's a murder mystery. You have been warned. Also, possible spoilers for season 4, but it's AU as well, so...but it was originally supposed to be based on Downton Abbey and then Agatha Christie got in my head and then this story happened. I'm sorry.

Chapter One – A Murder Most Foul

Lady Lydia Whittemore.

She pursed her lips and stared at her reflection in the mirror while Malia rolled her strawberry hair into an appropriate style. The name didn't sound bad, of course. The Whittemores were one of the most prominent up-and-coming families in England, and it would be foolish to upend her imposing nuptials because they were…imposing. Lord Jackson Whittemore, her husband-to-be, was handsome, came from a good family, rich, everything any woman could hope for in her married life. But the fact of the matter was she liked Lady Lydia Argent much better. She already had the title thanks to her mother's second marriage following her father's death, and she would rather stay at Beacon Hills with her mother and step-father and step-sister. Her sister Allison had become her best friends once their parents were married, and she hated the idea of leaving that behind to move to the Whittemore estate with Jackson. But at least she had it better than Allison.

Allison was, at that moment, draped across Lydia's bed in dismay, her dark hair already falling out of the careful pins Malia had put in it. Allison was supposed to be meeting her fiancé that night, at least the man their parents hoped she would marry, and Allison wanted no part in it. She wanted to run away with their father's footman, Scott McCall.

"Maybe he won't be so bad," Lydia comforted as Malia put the finishing touches on her hair. "Maybe he'll be handsome like Jackson."

"Maybe I'll run away before I have to marry him," Allison countered.

"You don't have to marry him," Lydia said. "It's just a preliminary meeting to see if our father likes his father well enough to let the union take place."

"And it's just taking place at the biggest ball of the season when everyone from here to Highclere Castle will be in attendance!" Allison insisted.

"Are the Carnarvons really going to be here?" Lydia asked. "I thought they were in Egypt."

"That isn't the point and you know it," Allison said. "The point is-"

"The point is you want to run off with Scott, and instead your marriage is being negotiated by our parents without your consent," Lydia said. "I know. They already got to me, remember?"

"But it was different for you," Allison said. "You weren't in love with anyone, and you like Jackson."

Lydia knew there was no reasoning with her when she was like this, and instead took the time to put in her pearl earrings. She didn't feel like correcting Allison's assertion that she "liked" Jackson, because she didn't, and instead decided to subtly repudiate him by refusing to wear the jewellery he'd got her as an engagement present. She still had to wear the ring, but that was for appearances' sake. She couldn't imagine ever being happy with a man who attempted to discuss scientific discoveries and completely misrepresented Gregor Mendel's principles of trait inheritance. Nor someone who got Pythagoras and Archimedes mixed up, especially not since she had read all of their works.

"Of course," Lydia said hollowly, pulling Allison to her feet and adjusting her hair for her. Sometimes she envied her sister for her height and her dark eyes and dark hair. Lydia looked far too Irish most of the time.

"The guests are arriving," Malia said, looking out Lydia's dressing room window. They rushed over and looked at the line of carriages stretching up the front walk. It was barely dusk yet and the party was sure to last well into the next morning, the majority of the guests spending the night. Not the Hales, of course, as they lived in the next estate.

After she'd followed Gregor Mendel's work about hereditary traits, Lydia had started to notice certain things about Malia. Technically, Malia was the daughter of their gardener, Mr Tate, and she was the same age as Lydia and Allison. Lydia had spent a good portion of their childhood teaching Malia the lessons she learned from her school books, since Malia didn't get to attend any sort of school, or sit in with Lydia and Allison and their tutor. But after she read about Mendel's work, she started to realise that Malia's nose and mouth and the shape of her eyes were almost exactly that of Peter Hale from the next estate. Lydia hadn't mentioned this to anyone, except Allison, and together they had inspected Malia's little sister for the same signs. They weren't there.

"I have to go back to the kitchens," Malia said. "Do you need anything else?"

"No, we're fine, thank you," Lydia said, smiling at her and squeezing Allison's hand. Malia curtsied and left.

"What if he's awful?" Allison complained.

"He won't be awful," Lydia promised. "They would never force you to marry someone awful."

They would only do that to me, since I'm the least favourite daughter.

"You're right," Allison said. "But I don't want to leave Scott."

Lydia smiled sadly at her and hugged her tightly. "We'll figure something out."

Small tables had been set up around the sides of the ballroom. Lydia knew the seating had been assigned meticulously by her mother, as Lady Natalie Argent had insisted on making her and Allison help so they could practice for their future hosting requirements.

"No, we absolutely cannot put Peter Hale at the same table as the Yukimuras," Natalie had insisted. "They have a daughter your girls' age who isn't betrothed and I shudder to think what sorts of deals that man would try to make."

That had been only one of a few examples. Peter Hale was also not allowed to sit near Lord Deaton, or Lady Morrell for reasons Natalie wouldn't explain. Lydia and Allison spent the entire month leading up to the ball grumbling about it as soon as Natalie was out of earshot.

Now the ballroom had been resplendently decorated and adorned with the finest garnishes the Argents could find. Festoons of pine boughs and holly hung along the banisters and Lydia frowned when she noticed the mistletoe. It was a horrid plant in her opinion. But she was probably biased after Jackson had taken advantage of its presence to kiss her.

As soon as they reached the ballroom, Natalie bustled over to them and pulled them towards Chris. Thankfully, Jackson was nowhere to be seen.

"You both look so beautiful," Chris said, smiling at them. "Lydia, where's your fiancé?"

"I haven't the slightest idea," Lydia said, scanning the crowd for the familiar blond hair. She didn't see him and considered it a blessing.

"Odd, I could've sworn he arrived earlier," Natalie said, a crease appearing in her forehead. "I'll have one of the footmen search for him."

She snapped her fingers and Scott materialised from the crowd with a bright smile. Lydia didn't understand Allison's attraction to him. He seemed too much like a puppy, with his big brown eyes and eager-to-please grin. Then there was the matter of his uneven jawline.

"We're missing Lord Whittemore," Natalie said. "See if you can find him, would you?"

Scott nodded dutifully and did his best not to look at Allison before he disappeared back into the crowd.

"Lord Argent."

All four turned to see who was addressing their patriarch and discovered an unpleasant looking man with spectacles and an uncomfortable sneer.

"Ah, Mr Lahey," Chris replied, shaking the man's hand formally. "And this must be your son."

The younger man standing behind Mr Lahey was tall and trim and stared at the floor while his blond curls covered his eyes.

"Yes, my son, Isaac," Mr Lahey said, dragging his son forward. Isaac Lahey winced at the grip his father had on his arm and looked up just long enough to say "how do you do" before he looked back down. He had lifted his head long enough for Lydia to see the black bruise near his hairline, marring an otherwise handsome face.

"Allison, why don't you and your sister take the young Mr Lahey to the drinks table," Natalie suggested. Lydia nodded in agreement before Allison could protest and took Isaac's elbow.

"What would you like to drink, Mr Lahey?" Lydia asked.

"It's Isaac, please call me Isaac," he said. He looked down at Lydia's hand on his elbow for a second and then went back to watching the ground just in front of his feet.

"Very well, Isaac, what would you like to drink?" Lydia asked.

"Nothing, I'm fine, thank you," he said.

"Nonsense," Lydia replied. "It's a party. It's the biggest Christmas party anyone's going to throw and I'm quite sure you're meant to be engaged to my sister."

Isaac and Allison both gaped at her. Lydia ignored them and handed Isaac a brandy.

"My father thinks so, yes," Isaac agreed. Lydia couldn't help but notice how his face twisted as he said "father."

"I'm sure you're very nice, Isaac, but I would rather not marry," Allison said. Lydia shot her a look and handed her a glass of punch, hopefully so that Allison wouldn't say anything else problematic.

"I'd rather not either, but I haven't often been in a position to control my own life," Isaac said, taking a sip of his brandy.

"Neither have we," Lydia said. "I shouldn't worry about it too much."

Isaac nodded and Lydia caught sight of the bruise on his face. She wondered if maybe he should worry about it, but brushed the feeling off.

"I hear you're betrothed as well, Lady Lydia," Isaac said.

"Lydia will suffice," Lydia said. "And yes I am. Although I have no idea where my fiancé has got off to. Mother sent the footman looking for him ages ago."

It wasn't like Jackson to miss parties, so she couldn't begin to imagine where he'd gone. Ever since they'd been engaged eight months ago, he hadn't failed to turn up to a single party. And he'd certainly never disappeared at one.

"I'm sure he just got lost attempting to find one of the maids," Allison mumbled. Lydia narrowed her eyes and Allison innocently sipped her punch.

"That or he's attempting to break into the wine cellar again and Mr Finstock is having trouble removing him," Lydia said, frowning at the memory of her fiancé coming up against their head butler. It had almost ended their engagement on the spot, but Jackson's parents had talked her father out of calling it off.

"Our parents certainly have excellent taste," Allison whispered, and Lydia hoped it was quiet enough that Isaac didn't hear her. Isaac seemed gentle, if not damaged, and she had no desire to damage him further, or let her sister do it.

The three of them stood by while the rest of the guests arrived. Lydia saw the Hales come in with their entourage and saw Chris's face tighten. The Argents had an uneasy alliance with the Hales, established only recently after centuries of battling over the same patches of Yorkshire countryside. The truce had been moderately upset by Peter Hale's existence.

Finally, the bell rang, and everyone found their seats. Isaac was shunted off to a separate table with his father and the Yukimuras, a very prominent family from Japan who had purchased an estate in England twenty years before. Their daughter was the same age as Allison and Lydia.

"Lydia, where is your fiancé?" Natalie asked as the footmen brought in the dinner.

"I have no idea, mother," Lydia replied, sipping her wine. "I haven't seen him all night."

Natalie frowned and then turned to make pleasant conversation with the person on her left. Lydia turned to Allison and was about to ask her what she thought of Isaac, when Scott crossed to their table in haste. He wasn't carrying any food, which meant he hadn't come from the kitchens like everyone else, and he was ashen. He paused next to Chris's chair and whispered something in his ear. Lydia saw Chris straighten up and look concerned. Somehow she knew it had something to do with Jackson, but she couldn't justify that suspicion.

"If you'll excuse me for a moment," Chris said, standing.

"Christopher," Natalie protested. "You can't simply abandon dinner."

"I'm afraid it's urgent, my dear," Chris replied.

"Is it about Jackson?" Lydia asked.

Both Chris and Scott turned and stared at her sharply.

"How do you know that?" Chris asked.

"I don't know," Lydia said. "It was just a feeling I had. Why?"

"Stay here," Chris instructed, following Scott out of the hall. Allison and Lydia glanced at each other.

"Mother, I'm so sorry, but I must go powder my nose," Lydia said. She excused herself from the table and saw Allison start like she meant to go after her, but the other man at their table – Allison's cousin from France, Lydia remembered – engaged her in conversation and Allison was stuck.

Lydia left the grand ballroom and crossed through the decadent entryway. Since everyone was eating dinner in the ballroom, it was entirely deserted. Because of that, she could hear the whispers coming from the grand staircase. She crept towards the corner and peeked around it to see her father, Scott, Mr Finstock, and the head of household, Mrs McCall, Scott's mother, standing in a line and staring up at something. Mrs McCall had her hand over her mouth.

With an increasing sense of dread, Lydia followed their gaze upwards and barely stifled a scream when she saw what they were looking at.

A body was draped over the banister at the top of the stairs, a gash in his throat. Because the body was hanging by its ankle from the banister, the blood had run from the gash all across his face and down to a little pool on the floor. While Lydia stared, the body started to slip. The four jumped backwards as it fell with a sickening crunch to the ground. Lydia would've known the man anywhere – Jackson Whittemore.

Just as an aside - Highclere Castle that Allison mentions is the actual castle where they film Downton Abbey and the Carnarvons are the family that lives there. The 5th or 6th earl (I don't remember) was responsible for helping Howard Carter fund his expedition to Egypt when he discovered Tutankhamen's tomb, and Lord Carnarvon brought his daughter with him when he went to Egypt - a daughter who was the inspiration for Evelyn Carnahan in the Mummy movies.