A/N: Basically, this is how I wish this scene had actually gone. And since I'm not the only fangirl in the world, I figured someone else would've wanted this scene this way as well, so I wrote it.
All dialogue is taken directly from the episode and therefore not mine. Anything from the episode is from the episode and also not mine. I just tweaked it a bit for my own pleasure. Credit Sir ACD, Moffat, and Gatiss.
"No."
Irene, still smiling from her victory asked, "Sorry?"
Sherlock repeated, "I said no. Very very close, but no. You got carried away." He stood and continued, advancing on her. "The game was too elaborate. You're enjoying yourself too much."
"No such thing is too much." Her smugness was practically rolling off her in waves.
"Oh, enjoying the thrill of the chase is fine. Craving the distraction of the game, I sympathize entirely, but sentiment?" Sherlock was centimeters from her now. "Sentiment is a chemical defect found in the losing side."
"Sentiment?" she asked, still confident, but curious as to where he was going. "What are you talking about?"
"You." His eyebrow twitched with the word.
At this point Irene knew Sherlock was dead on, but she wouldn't dare let on that fact. She was determined to get out of this with her money and protection intact. "Oh dear God," she said, hoping he wouldn't call her bluff. "Look at the poor man. You don't actually think I was interested in you. Why? Because you're the Great Sherlock Holmes, the clever detective in the funny hat?"
"No," he intoned in his rich, baritone voice. Sherlock leaned impossibly closer and took her wrist in his long fingers and whispered in her ear, "Because I took your pulse." His eyes were hooded and he softly ran his nose along the shell of her ear, and her smile dropped, surprise showing on her face. "Elevated. Your pupils dilated." He lingered there longer than he intended, still holding her wrist. Irene exhaled a shaky breath and he brushed his lips delicately against her neck as he reached for her camera phone.
Still standing milimeters from her, Sherlock murmured "I imagine John thinks love is a mystery to me, but the chemistry is incredibly simple and very distractive." Irene looked on the verge of tears now, for two separate reasons. He continued on, stepping back a few steps. "When we first met, you told me that a disguise is always a self-portrait. How true of you. The combination to your safe: your measurements. But this - this is far more intimate. This is your heart. And you should never let it rule your head."
Sherlock punched in the first letter - S.
"You could've chosen any random number and walked out of here today with everything you've worked for," he punched in the second letter - H.
"But you just couldn't resist it, could you?" he smiled a quick smile. "I've always assumed that love is a dangerous disadvantage," and the third - E.
"Thank you for the final proof."
Irene stepped incredibly close and grabbed the phone, but didn't take it from him. She was definitely near tears, now. "Everything I said. It's not real. I was just playing the game." Her voice wavered the tiniest bit. Only he would notice it.
"I know," he whispered, head bowed. The final letter - R.
"And this is just losing." A single tear slid down her cheek.
Sherlock held the phone up, displaying the passcode.
I AM
SHER
LOCKED
He handed the phone off to Mycroft. "There you are, brother. I hope the contents make up for any inconvenience I may have caused you tonight." His eyes, however, never left hers. He could read the distress in her shining emerald eyes and felt sorry for her. Completely ignoring Mycroft's response, he wiped the tear track from her face.
He turned away from her, unable to keep eye contact any longer. Sentiment, indeed. "Lock her up. I doubt she'll survive long without her protection."
"Are you expecting me to beg?"
"Yes." His response was immediate, and for a moment he questioned what he wanted her to beg for - her life or his affection.
"Please," her voice now broken, just like her heart. "You're right." He looked back, out of reflex, and couldn't look away again. "I won't even last six months." More tears fell.
Sherlock leaned in close and wiped the tears from her face once more. "Sorry about dinner," he muttered, then softly kissed the corner of her mouth. Her eyes fluttered shut and Sherlock quickly walked away and out the door.
She knew she'd never see him again.
Which was why she was so entirely surprised to hear her moaning text tone right before she was supposed to be beheaded. Her heart almost burst out of her chest when he'd said "Run!"