How Sage Became a Holmes//book the first (A Sherlock BBC Fanfiction)

Leverage?

I quickly pulled my phone out of my back pocket, about to dial Sherlock.
"I wouldn't do that if I were you, Miss Samuelson." Warned the cabbie. "Not unless you want Mr. Holmes to be reading the news tomorrow and hear about a young girl shot and left in a cab on the side of the road."
I had to remain cool, keep a level head. I refused to get myself killed in some stupid way and let Sherlock down, nevermind lower his opinion of me. I had to be sharp, keep my wits about me.
"You have something to shoot me with, I'm assuming?" I asked, trying desperately to keep my voice from shaking. He raised an eyebrow. Keeping a hand on the steering wheel and his eyes on the road, the cabbie pulled a gun from his jacket.
"Yes."
We road in silence to two unrecognizable, empty buildings standing side by side. As the cabbie got out and opened my door, keeping his gun pointed at me, I tried to conceal my fear.
"Sooooo, you're kidnapping me, right?" I asked casually. He gestured toward building on the left with his gun and I started walking.
"I am."
"Why?"
"Because..." He trailed off. Oh dear. This wasn't a many layered answer, was it? "I'm a business man, Miss Samuelson. I have an employer, a job." We walked into the building. "But I also know how people think. I know how to apply the right leverage to right person to work to my advantage." I bit my lip. Mycroft. He wanted to get to Mycroft. I kept my thoughts to myself, reminding myself to remain cool and that Mycroft didn't give a damn about me. He didn't care about anyone. "Have you heard about the suicides that have been goin' round?" I looked at him over my shoulder as we walked down dim corridor after corridor.
"Yes." He smiled, nodding his head.
"Well. Welcome to my work, Miss. Where I shall do my job. While applying leverage."
"Wait, what does that have to do wi-" My mind raced. "They're not suicides." I whispered, remembering what Sherlock had said as we turned into a dark and mostly empty room. "They're murders." The cabbie flipped the light switch and simply smiled at me. He then pointed to a corner of the room, his gun still fixed on me.
"Have a seat, Miss Samuelson." I sat in the corner, and the cabbie pulled a roll of duct tape from his pocket and bound my hands.
"Are you going to murder me?" I asked, trying to sound nonchalant and casual.
"Miss, haven't you been listening?" He asked, sounding quite exasperated. "You're my leverage. I can use your disappearance to cloud the thinking of my next victim, to arouse suspicion. To weaken the strong. Emotions are a very powerful tool, Miss Sage. If you know how people think and feel, you can find their weak points. You can manipulate them." I scoffed in his face.
"You obviously don't know me or the people I associate with, then. Emotions are a weakness as you say, and if you're going after who I think you are, you won't have much luck." He ripped off another piece of duct tape and placed it over my mouth. I rolled my eyes. Great. I thought. This is just. Great.
"Don't offend me, Miss Samuelson. I know what I'm doing. This is my living, after all. A word to the wise: you don't make much drivin' cabs." He turned off the light and closed the door.
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Back at Baker Street, John Watson made his way up the stairs to 221b. Sherlock was lying down on the couch, eyes closed, fingers steepled under his chin. John stood in the doorway a moment before asking,
"What are you doing?"
"Nicotine patch." Said Sherlock, sighing. "Helps me think."
"Are those...three patches?"
"Mm hm. This is a three patch job." A moment of silence went by as Sherlock seemingly resumed his deep thinking.
"I just met a friend of yours." Said John.
"A friend?" Sherlock's sounded shocked.
"Mm, an enemy."
"Oh. Which one." Asked Sherlock.
"Your...arch-enemy, according to him. Do people have arch-enemies?"
"Did he offer you money to spy on me?" Inquired Sherlock, one eye open.
"Yeah, you, and more specifically Sage."
"Did you take it?"
"No." Replied John. Sherlock sighed and closed his eyes.
"Pity. You should have taken it, we could have split the fee."
"Who is he?" John asked.
"The most dangerous man you've ever met and not my problem right now." Another silence.
"Well?" Asked John. "You asked me to come, I'm assuming it's important." He sounded irritated. He probably was irritated.
"Oh, yeah. Can I borrow your phone?"
"My phone?" Asked John.
"Mm, don't want to use mine. Always a chance the number will be recognized." 
"Mrs. Hudson's got a phone..."
"Yeah, she's downstairs. I tried shouting, she didn't hear me."
"I was on the other side of London!" John shouted. (John is now reading over my shoulder and insists he wasn't shouting, he just raised his voice. I'll leave the conclusion to you.)
"Oh, there was no hurry." Sherlock assured. John sighed, obviously exasperated, and pulled his phone out of his pocket.
"So, is this about the case?"
"Her case..." Sherlock muttered. "Her suitcase. The murderer took it, which was his first big mistake. On my desk, there's a number. I need you to send a text. Two texts, rather."
"You've brought me here...to send a text." Said John.
"No, weren't you listening? Two. Two texts. The first to Sage. Her number is already in there." John scrolled through Sherlock's phone down to the "S's". "Now type 'He's offered John money to spy on us. And where the hell are you?' Go ahead and send that, then-"
"Hang on, hang on!" Exclaimed John. He finished typing the first text and sent it. "Ok, now the other one?"
"The number is on my desk. These words exactly: What happened at Lauriston Gardens? I must have blacked out. 22 Northumberland Street. Type and send it, quickly." He leaped up from his position on the couch and paced around the flat a moment before settling in his armchair. He didn't remain there long before he got up again and retrieved the suitcase from under the desk.