You may have read the first two episodes as that was a different book. It was all a bit rushed - I don't know why they didn't do the first book or the second and covered one in four episodes which would have been far better
The wife reads Billingham books, but hadn't read "In The Dark" yet (but has it), so gave the TV series a swerve, looks like she made the right choice. Also a fan of Stuart McBride books too.