"Ah--" Christianity. Nico thought that his mother had been a follower of that; he vaguely remembered church services as a child... But it was never something he'd given real thought or study, especially since learning his true heritage. His only experience of an apocalypse was, well, that epic gods-versus-Titans battle last August. He guessed the Christian apocalypse didn't involve skeleton soldiers on fire.
(Or maybe it did? He'd read the Bible later, maybe.)
His frown deepened as he listened to the explanation, particularly when River mentioned dead people not being dead. He held his breath for a moment, trying to extend his senses -- but no, she still felt alive to him. Either she was lying and had never died, or was being truthful and had died in some unimaginable world that was beyond Hades' influence. He swallowed; he wasn't sure which option might be best.
"Other worlds," he murmured. River didn't just mean Roman v. Greek; this was much more serious. He tucked his thumbs in his pockets and glanced around nervously.
"Say I believe you. Who's Lucifer? Why's he in a cage -- and how do we make sure he stays there?"