The Fire Within — Graham Watkins

The winners had one thing in common, a lifetime of terrifying, blood-soaked nightmares. But now they hoped to escape all that, to cast off the pressures of civilization in a sun-drenched paradise by the sea. Soon, their inhibitions faded away; their wildest erotic fantasies come true. Then the horror began-the strange native rituals, the forbidden urges, the gruesome human sacrifices, and worst of all.... The monstrous truth behind their own unearthly passions.