Sherlock forced Greg to leave, insisting that we'd be right behind him. At the same time, I was going through every last line of my medical knowledge trying to come up with a plausible cause of death that would explain why Zariel just seemed to drop dead.

The second the door shut, Sherlock began to bounce around the flat, his blue dressing gown flapping behind him.

"A case, John!" he exclaimed as he grabbed his cup of tea that I'd forgotten I was holding. "A nine, at least, from the sound of it." He flounced past me, because that was really the only word for it, into his room, shutting the door behind him.

Maybe Mrs. Hudson would have an idea.

Sure that Sherlock wouldn't emerge for a few minutes (he always took forever dressing, especially after he'd spent days moping around the flat), I ran down stairs and knocked on Mrs. Hudson's door. She opened the door a few moments later.

"John! What a surprise. Come in. Is Sherlock getting on your nerves, dear?"

I stepped through the door and waited until it was shut before pulling out my wand and casting a Silencing Charm.

"What's this all about, John?" she asked, eyeing my wand. She rarely saw it, and I rarely pulled it out around her. Sherlock usually burst in on us whenever I was visiting. He felt like he was being left out of something important when the two of us were talking.

"Sherlock just got a case. It's an Avada, I'm almost positive."

"Oh dear. That's no good."

"No, it's not." I leaned against the door. My shoulder was aching from being at Hogwarts. All the magic in the air made it ache. "I'm trying to come up with something to tell him, but I'm drawing a blank."

Mrs. Hudson clucked. "Well, he can't find out. He is a Muggle after all. Sometimes I think he suspects something is up with my flat, you know, the way there's never any dust, but he never has figured it out."

"No, but he's going to be unbearable if he doesn't solve it. You know how he gets. I think this time it will be one of the worst."

"Don't worry, John, dear. I've seen him at his worst; you haven't. It's nothing you can't handle. He's so much better now that he's got you."

I sighed. She was still on about that. Checking the time, I saw that I'd been down here about five minutes. Sherlock would be ready to leave soon.

"I've got to go, Mrs. Hudson. I'll let you know what happens."

"Be safe, dear."

I nodded as I left her flat and headed back up the stairs. As I entered the flat, I didn't see any sign of Sherlock, but the bathroom light was leaking out from the gap beneath the door. He was probably messing with his hair. Since I was still dressed, there was nothing for me to do but wait.

Maybe I could say she was suffocated. Still, there probably wouldn't be any physical signs. No bruising on the face or neck or any sort of lacerations on the inside of her mouth from her teeth.

I scrubbed my hand across my face. There was a reason I left the magical world, but now I was being forced back into it with my mad Muggle flatmate. It's not like I could just tell him I was a wizard. Even if I could convince him magic was real, there were about a dozen Ministry rules that kept me from telling him.

There's the exception for significant others, a voice said in my head.

Just then, the bathroom door opened, scattering my thoughts. Probably a good thing. That was the sort of thing I didn't need to be thinking about. After all, it would never happen, and even if it did, I'd be telling probably the most rational human alive that magic was real. That would go over so well.

"Are you ready, John" Sherlock asked as he slid the Beltaff coat on over his well-tailored suit.

"Yeah," I said as I stood. I joined him at the coat rack as he was winding the blue scarf around his throat.

I followed him down the stairs and out the front door without a word. Not that speech was necessary. Sherlock was a whirlwind of energy, thoughts and deduction streaming from his mouth. I really hated when he didn't have a case. Partly because he was irritating as hell, but mostly because all that energy and intelligence turned inward to tear him apart. Sometimes I wondered if I slipped him a Draught of Peace, he'd manage the boredom a little better. Technically, it was okay to use potions on Muggles, but with that big brain of his, who knows how he'd react. Not to mention my potion making skills were rusty. Didn't want to poison him.

Finally, we arrived at the scene. Lestrade was waiting outside, his arms crossed tightly. He was irritated. I glanced at my watch. It had been nearly half an hour. I really didn't blame him.

"Where were you?" he asked as Sherlock glided across the pavement toward him.

"In there, I assume?" Sherlock asked, ignoring the question. Lestrade nodded tersely and turned on his heel to lead the way.

"She was found by a couple of teenagers who were trying to, er, you know…." he said, clearing his throat awkwardly. "Anyway, we couldn't find the cause of death. She has a couple of bruises and a nasty scratch, but nothing that would have killed her."

Sherlock ducked under the police tape, then held it up for me. I followed him around the last corner where I saw the body of a girl lying on the ground. She had long dark hair and was wearing Muggle clothes.

Sherlock bent over the body. "Late teens, probably sixteen. Fashion is out of date, late 90s." He went around to the other side and looked at her right hand. "She went to some sort of boarding school up north, wore a uniform, and," he paused for a moment, "wrote everything by hand with something other than a pen or pencil." He pulled up her sleeve on her right arm, then left and furrowed his brow. "Raised by traditional parents who insisted that she follow their way of life. This looks like it might be some kind of religious tattoos." He stood and looked at me. "John, cause of death?"

I took a pair of gloves from Lestrade, who was leaning against a wall watching. He was used to this now. I pulled the gloves on with a snap and knelt next to the girl. Looking closely, I saw no sign of death. I checked her over for anything and everything: suffocation, head injury, poisoning, anything. I couldn't find anything. Just the signature look of terror that one has when they know they are going to die from a curse with no way to stop it.

I was about to stand when I saw the bottom of the tattoo peeking out from beneath her sleeve. It looked familiar. Curious, I pulled it up. Dread washed over me. It was the Dark Mark. But what was she doing with it? She was born long after You-Know-Who died. Only former Death Eaters had these.

I glanced up at Sherlock. He must have seen my expression. He didn't understand. "Can't find anything definitive," I said. "Maybe poison?"

"That wouldn't explain the expression on her face." His gaze swept over me again, then walked back to Lestrade. He knew I knew something. I followed behind him, slowly peeling off my gloves.

"I'm going to need sample sent over to Barts. There is no clear cause of death."

"Hold on," Lestrade said as Sherlock started to turn the corner. "Explain."

Sherlock huffed and settled back on his heels. "What exactly would you like to know?"

"The boarding school, the parents, and the tattoo."

"Easy. Her tan lines indicated that she wears the same clothes every day. Strong line, especially on the neck and the wrist. She's still pale, so she doesn't get a lot of sun, especially since she isn't in the south. She has callouses on the fingers of her right hand from writing, but they aren't from a pen or a pencil the callouses would be different. As for the parents, she is wearing clothes that are more than ten years out of style. Her parents would never let her dress like this; she's bought them on her own, but she hasn't had access to current fashion. The tattoo lacks artistic choice, especially for a sixteen year old girl. It isn't affiliated with any gangs, and there are religious themes. The serpent, the skull, and the infinity sign. Perhaps an occult group. Now if that's all, I'm busy."

Lestrade nodded, and Sherlock whipped around the corner.

I paused. "Thanks. He was starting do experiments. I think he was going to go after my jumpers next."

"No problem. I really didn't know where to start with this one. But he likes the strange ones."

I nodded. "I'll see you at the pub Saturday, yeah? Assuming he's not dragging me all over London?

He nodded, and I turned the corner quickly. Sherlock was waiting next to the road. I ducked under the police tape and hurried over to Sherlock, who was hailing a cab.

A black cab pulled up to the curb. It was like magic, how Sherlock was able to get a cab whenever, wherever. We were both silent the entire way back to the flat.

What was that girl doing with the Dark Mark? It wasn't a true Dark Mark. Only You-Know-Who could brand people. But who would choose to take that mark. Only someone who grew up around the Dark Arts. Somehow, her involvement in the Dark Arts didn't seem so surprising anymore.

I could feel a sharp gaze on me, and I looked up. Sherlock was staring at me intently, like he was trying to figure something out. I raised an eyebrow. Sherlock responded with a slight tilt of his head and a shrug. I shook my head then looked away.

As the cab pulled up in front of the flat, I realized that I just had a completely silent conversation with my flatmate.