Has this cross over happened before? Would Wilson and Maberry have to agree on such an appearance.

Not to my knowledge. Maberry has occasionally referenced SIGMA Force from James Rollins's books and Seal Team 666 from the series of the same name by Weston Ochse. Jack's appearance marks the first time another author's character has appeared "onscreen" in the Ledger series.

For my part I see Maberry's setting as a kind of ultimate action-horror crossover world. You can assume that something like what happened in the various other authors' books happened here, but not that exact thing. So you don't have to read Nightworld and wonder "Why didn't Joe Ledger and RTI show up for this?"

Thanks. I think I will check out those other series. I have a large queue of Repairman Jack Audible books that I got when they were doing a fantastic sale, but I also have some credits to use. Joe Ledger was my first entry into action-horror, and I really like it (would like to see more movies made in that vein as well).

From what I have read in the past, I would assume that Mr. Wilson would have had to agree to let Mr. Mayberry actually use the Jack character. It's not like one of Mayberry's characters are just referring to Jack, he is an actual character in the book. I just got to that point in the new Ledger novel and was very surprised. Had to re-read that chapter to make sure I was reading it correctly. He even refers to him as "Repairman Jack" towards the end of the chapter. Can't wait to see where it leads.