Pandora's Hideaway by Lizbeth Dusseau.
Rules are suspended and the game's a risky, dangerous one in Pandora's Hideaway - a South Seas tropical paradise owned and ruled by an anarchist and daunting sexual Dominant, Carlos Sanchez. After being caught having sex with her fiancé's brother, Jack, Mariel Fitzgerald's life takes a sudden twist when she begs the black sheep brother to take her with him on assignment to this faraway place with the strange sounding name. Immediately on arrival, she's shocked to find herself in a world where women accept their roles as slaves to men - there to be silenced, exhibited, used and determinedly forced to surrender. Mariel wages war against her unwavering host - and loses. Even as Jack pushes her into compliance, his own submerged and deviant sexual desires find a perfect playground in this out-of-the-way locale. Once Mariel relents to the darkness inside her, she gives herself wholly to Carlos, only to find that behind this paradise of sexual gratification is a sinister game designed to make her a perpetual, sexual captive and subject to the whims of her despot lover. Defiance only earns her a trip to Percy's prison - a sexual concentration camp for the resistant submissive. Rescue is impossible - or so it seems.