Spike chuckled - humorlessly as it may have been - when she insisted that she could stop him. He knew that she was a formidable opponent, had witnessed a small taste of her power and suspected she was stronger than what he'd seen, but also knew his own strengths. It was his general assumption that he could equal or overpower her fairly easily in a fight, and he really didn't want to have to test the theory. Who would want to destroy their own (claimed) sister?
"You won't be," he said, his eye twitching briefly with the thought that he might lose control enough to hurt her. Or make her get caught in the chaos that he planned to cause. He glanced down the corridor again, feeling the urge to get the killing over with and hopefully release some of the anger (and other, unspoken emotions), but refused to walk away when she was speaking. If it could, somehow, be the last time they spoke...
His eyebrows furrowed in response to the number of messages sent. He didn't know much about the network's nuances, but if she felt that many messages were necessary... Could she possibly be attempting to contact anyone other than someone who couldn't reply? Simon, then. Her brother seemed the most likely of those who'd died on the island. That she hadn't received an answer was disturbing. It seemed to point toward the 'they're all dead now' theory.
"River..." He paused, taking a deep breath to calm the anger evident in his tone. He normally didn't care if he lost control, but he'd promised to keep her whole. Even if that was no longer possible, the least he could do was avoid further breaking the poor girl. "...It's not a question."
He finally closed the door and glanced at her, hoping to convey through his expression (and, after what she said of thoughts, suspecting she would understand perfectly) that he didn't want to have to hurt her. This was something he had to do, for himself and for the honor of those stolen by the old island. In his current state of mind, it was something he had to do; and he fully intended to act upon the plans.
Shoving his hands into his pockets, he stepped away from the door, pausing only to gauge River's reaction. He fully expected her to back down. Or maybe he just hoped she would. When he thought about it, he doubted she was any less stubborn than him.