There was Christmas travel. Whaddayou want from me?
It took Child years to get there, but this one’s actually a prequel: It takes place a few months before Killing Floor, and tells the story of how Reacher came to leave the Army in the first place back in 1997.
Child’s gotten good at this, which is more or less what you expect with any series. If you look at the early books here, and compare with the early entries in Sue Grafton’s Kinsey books or Robert Parker’s Spenser books, you see commonalities: brisker, less fleshed out plots and characters, generally less interesting stories. Fast forward a few years, and the stories get some meat on their bones. (Hell, it even happened with the Potter books.)
The troublesome note is that there are only two more books currently available, though a 19th entry is scheduled for release next October.