Following the death of his family in an aeroplane crash, underwater salvage expert John Talbot (Barry Newman) hatches an elaborate scheme to bring those responsible to justice. After staging the phony murder of a police officer, he kidnaps Sarah Ruthven (Suzy Kendall), the heiress to a petroleum fortune. His exploits attract the attention of the criminal mastermind behind his family's demise, who hires him to recover the valuables aboard a recently crash-landed plane.