Code Name : Chaos (A BBC Sherlock Fanfiction)

XL : Letter (Sierra)

I stared at the note in front of me. He couldn't stay here, he couldn't. Suddenly, the letter was ripped from my grasp and I whipped my head around to see Irene standing next to Sherlock, a smirk on his face.
Mi hermana,
I'm coming to stay
M.L
Sherlock stared at me for a moment. "Your Brother ?" He asked. I nodded, "Mateo Leone." I said without realising. I froze as a wicked smile spread over Irene's face. Sherlock stared at me in amusement. "Not Sierra Lopez then, Sierra L-"
"-eone." I finished for him, "My parents decided to name me after a country, how funny." I deadpanned. He chuckled. He'd changed in the few weeks we'd been back in London. He was happier, laughed more. I glared at Irene as the two of them laughed. A jab from my elbow straightened the detective, "Ouch ! Ok, ok tell us about your brother." He said rubbing his arm. "Let's just say he's dangerous." Irene leaned forward. "You can tell us." She purred. I shrank back, blushing. What is wrong with me ? I thought. "I'm the outcast of my family, simply because I'm not associated with any sort of crime." At this point Sherlock cleared his throat.
"Excluding my brief stint as the Crimson Rose !" I protested. He nodded before springing out of his seat. "Alright, that's enough about you, let's talk about me, or more specifically my newest case." I rolled my eyes as he pranced around the living room, eyes filled with childlike glee. "We're trying to catch this massive drug cartel. El Diabolo. They're infamous for their insignia, a wax seal of the devil. They send it to people who fail to deliver their payment."
"Sherlock maybe don't act so happy ?" I suggested with a smile. He nodded. Just then there were three sharp raps on the door. I paled as I stared at it. "Mateo ?" Asked Sherlock. I nodded, apprehension rendering me unable to speak. He opened the door, and Mateo walked in just as I remember, scruffy hair, checked shirt, expensive watch. He opened his arms with a flourish. "Little sister, did you miss me ?"

I walked towards him, awkwardly wrapping my arms around him. Irene walked up to him, "Irene Adler." She said with a shark-like grin. I felt something akin to jealousy, as I watched her latch onto his arm and guide him to his room, captivated by his looks like everyone else. But why am I jealous ? Irene's trouble, I can't fall for her. I internally scolded myself, only looking up when Sherlock walked up to me. "Wee bit jealous are we ?" I shoved him lightly, and he flashed me a knowing smile, which maddened me even more. "Shut up." I said, flopping onto the couch.

Irene
I felt sick as I laughed like a simpering fool, pretending to hang off Mateo's every world. It was for a case but it was still humiliating. Mycroft had told me the Leone family would be coming to London, but I didn't realise they were related to Sierra. Or that Sherlock was trying to catch the Diabolo cartel as well. I tried not to show my anger as I clung to his arm, flashing him seductive glances and smiles. Still, I supposed Sierra's look of jealousy almost made it worth it. Almost.

AN : So, what do you think of Mateo, and Sierra's developing feelings for Irene ? Hope you enjoyed, love you guys 😘😘😘