The Dark Mermaid: Siren's Song - The Dark Mermaid, #1

In The Dark Mermaid: Siren's Song, Madelaine travels to a remote Thai island which is promised to be incredibly beautiful and uninhabited, to renew herself after the end of a disastrous relationship. Madelaine's fellow backpackers on the island, Marco, Matias, Arvid, and Eugenie are also seeking renewal after difficult times in Europe. The island is beautiful as promised but not uninhabited and the backpackers must engage in an epic struggle with the inhabitants of the island.
In the course of their struggle, Madelaine starts to develop a relationship with one of the other backpackers but finds that she has a love rival from the island, The Dark Mermaid.