"I know enough," Joan says. She really doesn't know everything, and doubts that she ever will. She doesn't deny that Moriarty is brilliant, that her mind is complex in its depths. She was just able to recognize the woman's weakness. That she would take a chance, expose herself to swoop in and save Sherlock when he was at his weakest.

"I don't expect you to lie to me. I do expect you to try to manipulate me. I don't blame you for trying. I'm just telling you now, it won't work."

She looks up at the man guarding them. "Maybe next time they can handcuff you to the table, and then we can shake on it. For now your word is good enough." As much as that means. She doesn't trust Moriarty as far as she can spit her, but if she can help them save lives, then she'll give this a try.