I enjoyed this quite a lot. The sleuth in this series is actually Charlie Harris, not Diesel the cat. However, Diesel /was/ a presence, and I was pleased to see that the author made the cat intelligent, but not excessively so. I love my Maine Coon, too, but I don't think he'll be solving crimes anytime soon. ;)
That being said, I appreciate Ms./Mr. James' attention to detail with regards to Coon personality traits. Diesel was charming to read about(However, I hope the next book doesn't mention Diesel's size quite so often. The first two times were enough. Yes, Coons are larger than the average house cat. I don't need to be told that every time someone new meets Diesel for the first time).
As for Charlie Harris, it was refreshing to read about a character who was simply a nice guy. Antiheroes--in all genres--are in these days, and while those types can be fun, sometimes it's a relief to have a protagonist who genuinely wants to help, without having to be dragged into it.
Overall, Murder Past Due was a good comfort read. I look forward to the next book in the series.