The murder. [ The answer comes without hesitation. He's aware Dean has a brother—has met him, by this point—but he remembers what Dean said when Geralt pointed out that the path this curse will lead down is likely more killing. ] The blade was used to kill a creature that couldn't be harmed otherwise. In exchange for using it, he received the mark.

[ Wait. Does that mean the blade could—?

Alucard disrupts his thoughts before they can finish. Geralt flicks his gaze up. It's clear he's been going through this bullshit for awhile, that he's not gotten far, and that he really wishes it weren't his fucking problem. In a way, it isn't. It's Dean's. But Dean's a friend, a close friend, so.

It is his problem.

He huffs. Yeah. About that. ] Regretfully, he's an idiot. Didn't exactly review the terms in detail before accepting. Or at all.

[ So. Theology it'll have to be. ]