Still See You Everywhere by Lisa Gardner

 This is a Frankie Elkin novel and I'm not sure that I've read any of the other ones from this series, though I did enjoy this one. It is quite a page-turner.

Frankie Elkin finds lost people. She gets hired by the lawyer from a woman on death row (Keahi)  to find the woman's younger sister, Lea. Frankie ends up working on an eco-friendly construction project on an atoll in the middle of nowhere, owned by a wealthy man who is supposedly Lea's guardian--and was also Keahi's abusive ex. Frankie finds life on the atoll very hard, very hot, and very unnerving because she's not sure whom she can trust. And things spiral out of control when the wealthy man and Lea show up on the atoll. Couldn't wait to see how it all turned out.