The Master remained calm, his eyes showing no fear. He continued to stare him down, pushing down any terror he felt when Valek's fangs were shown. If he was bitten, he wasn't sure he'd regenerate.
He glanced at the Doctor quickly, checking up on him again, before bringing his gaze back to Valek.
"You're the one going to hell, my friend."
And with that, he pressed the button, operating his laser screwdriver against his head.
OOC:It's up to you how you want him to be affected. I've posted before hand to make it look like the setting isn't on kill, so however you want him to react is up to you.