Question: You recently stated that you had originally planned on writing Proven Guilty before Dead Beat. What do you think you would've had Molly doing during Dead Beat, if that had happened?
Molly would have been doing basically what Ramirez was doing. It would have been her on the back of a dinosaur, and so on. Getting into trouble. The kind of assistance she lended would have looked a lot different, and a lot black magic-ier. But that would have basically been her job, if we'd done it that way.
But, as it was, my editor called me and said, "What's the next story gonna be?"
"Oh! It's gonna be all about Molly and, you know, she's gonna be getting into this, and Harry's gonna be picking her up as an apprentice."
And she's like, "You know Jim, you might wanna think, for this next book, you might wanna make your story a bit... bigger, a bit broader, a bit more solid."
I'm like, "Are you saying I'm going to hardback!?"
She said, "I didn't say that... But maybe you should think about it just in case it happens."
And I'm like, "Oh, okay. So. Um. T-Rex."
Source: Dragon Con 2014 - An Hour with Jim Butcher Panel (Timestamp: 7m12s)
Date: August 29, 2014