I’ll start off with suggesting that you start with the first book. I had this one specifically recommended to me and I really felt like I was dropped into the middle. This one focuses on Gwen and Alex in the aftermath of what had to have happened in book 3.
But, to catch you up, it appears as though the serial killer is selecting girls that look similar to Piper - whom, I’m going to assume was the FMC in the prior books. This one is NOT focused on Piper and her love interest, the other Corbin brother, Emeric.
So, in the aftermath of…prior books. Gwen is back at home with her husband Alex Corbin (the married part seems to be new-ish), recovering from her ordeal and trying to get back to life as usual. Her husband is treating her like she’s in need of healing … and denying her (her trauma did not include sexual assault, thankfully) marital rights. So there’s some fun and playful banter as the two try to navigate a new normal and overcome the emotional aftermath of, well, at first she can’t fully remember. But as we progress through the book, and she progresses through her healing process, she remembers more and more (and the police discover more and more).
In the background, shadowy figures plot…and focus on a new target.
It had fun and light moments and dark and violent moments. It’s clearly part of a larger, more complex storyline. Which isn’t to say that you’re lost, trying to start with Book 4, but I wouldn’t say it’s at its best as a standalone. Either way, it’s enjoyable as a romantic suspense tale with a darker side - combined with a lighter side of love and healing.