Agreed. Monsters are scary when they look like monsters - all imposing and frightening, but that's the thing, you know they're monsters. You at least know what you're up against. When the monster doesn't look like a monster, when it looks like just another person, certainly not evil, someone you'd lower your guard around, that's when the monster's scariest - because you would have never known, you are not prepared.
It starts with a song – Lilith’s song – and a little help from Arrianne who tells him that Lilith ended up in hell. Cam goes out in search of Lucifer, but he doesn’t have to look far. Lucifer knows what he wants, so he shows Cam what he wants to see. But Cam isn’t satisfied with just a glimpse of her, especially because she is in Hell. So he makes a deal with the devil.
Guide to the Nine Circles of Hell (Dante's Version)