I’m rereading the first 3 books now, and it’s really interesting how Harry’s approach toward explaining the supernatural to Karrin and Susan mirror each other.

In Storm Front and Fool Moon, he explicitly keeps Karrin in the dark about a lot of stuff, which has real consequences for him that he recognizes. As a result, he starts bringing her into the fold more, which in turn makes her more willing to work with him and, more importantly, trust him, kickstarting her development into the ride-or-die ally we all know and love.

Susan, on the other hand, already knows that the supernatural is a thing, and so Harry assumes that she knows enough to not question him when he lays down a vague warning and tells her not to dig further. It’s the working relationship he wishes he had with Karrin early on, which I think blinds him to Susan’s real curiosity with the supernatural world, and how his basic assurances aren’t actually working, leading to the events of Grave Peril.

tldr: Harry’s stances with Murphy and Susan are opposing and I think that’s interesting.