Isabelle is 28 in the first book and finally starting to grow up a little. She had been a juvenile delinquent (literally) as an adolescent, but had followed a straighter path once she hit 18. Her parents run a PI firm and all of the kids worked in the firm as teens, learning the business. David did not enjoy the family business and went on to law school. Isabelle loved the business. She also remained in her parents house, albeit in an attic apartment until she was 28. Rae was 14 years younger than Isabelle and 16 or so years younger than David. Rae also looks young for her age.
The first book is framed around the story of Rae's disappearance, and much of the information seems to come out as a result of Isabelle's questioning by Inspector Harry Stone.
The second book revolves about Izzy's inability to let a case go, even when everyone around her tries to convince her otherwise.
The third book revolves around Izzy's soul search about whether or not she is really cut out to make PI work her career. It also involves a lot of changes in her life.
I loved all of these books, which is probably kind of obvious because I read all 3 in 2 days. It was literally an I laughed, I cried kind of thing. Izzy is a very sympathetic character. To me she seems like what Sue Grafton's Kinsey Milhone could be if she would try to act a little more human. There is no doubt that Isabelle is a flawed character, and she at least begins to come to terms with some of those flaws by the end of the third book. She changes and grows and see the effect she has on the world. Over the course of the three books we also develop a nicely rounded picture of the other members of Isabelle's family and friends.
The mysteries themselves are ok, they aren't too hard to figure out. I was able to put the clues together myself before the reveal, which I kind of enjoy more than the kind of ending that just seems sprung on you out of nowhere. But, the mysteries are fairly compelling. It's also nice to read a series where the main character doesn't have to put herself in mortal peril in order to figure out the mystery. Actually, some of the side mysteries involving Izzy's family are more challenging to figure out than the main ones.
I highly recommend the Spellman Series by Lisa Lutz. They make up a funny, entertaining mystery series with great characters that you can root for. I can't wait to see where she takes the series next, it seems like it might be at a pretty good turning point.