The Pisachas Retribution by Lee Cushing

When two teenage girls are raped by brutish mercenaries and the witnesses murdered while the thugs are helped to evade justice. Forrest King and Catherine Jordan track the culprits to Greece where they infiltrate the private island of Stefano Balasi, the crime boss who employs the thugs. Determined to make the mercenaries pay for the rapes, Forrest, Catherine and their friends back in England soon find themselves the targets of an ancient demonic cult whose followers have a taste for human flesh.