Invisible is a quick cozy mystery read that seems to have reviews all over the map, from one star to five. It is an overtly Christian mystery and the summary on Amazon does not mention this. I'm sure that accounts for some of the review disparity.
If you are taking it just as a cozy mystery, it would fall on the very light and fluffy end of the spectrum. Ivy Malone is an older widow who feels like she's pretty much invisible to most people these days due to her age. She still has a lot of curiosity and energy and wants to be doing something so when a mystery happens right in her neighborhood, she begins investigating on her own.
I had a really hard time getting into this one and almost quit on it. Like most readers, I hate to give up on a book and it did get much better as I read. It started out feeling very shallow. The Christian viewpoint is very noticeable and even though I'm a very committed Christian, it felt a bit heavy-handed at times. The mystery was not difficult to figure out.
Even with the problems I've mentioned, I was enjoying the book by the end. I enjoyed the characters as I got to know them. Not a must-read but not a complete waste of time. I'll finish the series if I run across them but I probably won't actively seek them out.