I find Jayne Castle (and JAK/AQ) books to be such comfort reads for me. I know they don't work for everyone, I know that there's a bit of a formula, I know that they're low angst (actually that's a plus for me) and there aren't a lot of hurdles typically to the relationship. But I find them so entertaining that none of that matters to me.
This one was typically entertaining for me. Alice is plucky and a bit down on her luck. But she has one of my favorite dust bunny companions ever in Houdini. Drake has been burned (somewhat literally) by a relationship before but can't help but be intrigued by Alice. He comes to her for help because he needs her type of talent to help stabilize what's been happening in the Preserve. While I think you can read the Rainshadow Island books separate from the other Harmony books, I would read the other books in the series first. You don't need the background for the romance but the larger plot had been developing over the course of the series.
So Alice, Drake & Houdini make their way to the island, have adventures and fall in love (Drake & Alice that is, not sure about Houdini but her certainly makes some friends at least). The mystery plot of what's been happening in the preserve and who is behind it spools out at a good pace. I can't glom these books because then the similarities do stick out more for me but I do enjoy them whenever I do read them.