A serene Caribbean cruise on a tramp steamer (their long awaited idyllic vacation) turns into a complete nightmare for the Ravynne sisters when they are lured to Purgatory Island by fellow passenger, Graeme Leighton, who believes they can rid him of the dark entity possessing him.
Trapped there, with no hope of rescue any time soon, the sisters square off against the monstrous evil that inhabits the old Spanish fort with its myriad secret rooms and passages haunted by the ghosts of the very long dead. Fighting for their own survival, they uncover , one by one, the dark secrets that lie at the heart of Purgatory Island....murder....lust...betrayal and a centuries old promise that must be kept at any cost...perhaps even the ultimate one.