There was a moment, a brief split second passing of time, when Obi-Wan saw himself responding to her raised weapon with instinct and passion instead of peace and composure. It was a frightening glimpse into a reality that wasn't so improbable. He wouldn't have been the first Jedi in history to turn to the Dark Side, after all. In this flashing image, he drew his lightsaber and swiped at her arm, severing her hand from her body before she could pull the trigger. And then he lunged forward, plunging the blade into her chest, eliminating the threat to his person. In this single possibility, he killed her indiscriminately. And he didn't feel anything afterwards.
Of course, that didn't happen.
Instead, he held his ground, standing calmly in front of her as she held the gun, aimed at his head. His physical reaction was no reaction. And just as the flash in his thoughts, it had not been planned. Seeing this possibility in his mind caused his heartbeat to quicken and he found that his body was unable to move. He felt lost and alone, disconnected from the Force. It was as though he were already the ghost of the man in those books.
He stood there, immobile. Not thinking. Only waiting. And then she returned to her senses and Obi-Wan relaxed, but only slightly.
After her apology, Obi-Wan placed Luke's book on the table and sat down in a chair across from her.
"There's no need to apologize. I sense a great disturbance in the Force over these books. Many of the residents here are feeling the conflict of what the library has to offer. Myself, included. It is only natural that you are not feeling yourself. I, too, am trouble by what I've read here today."