When Dr David Audley - MOD historian and spy - receives a tip-off from the CIA of a covert KGB operation involving the Vengeful, a long-forgotten, nineteenth-century French navy vessel, he sends his insubordinate protégé Paul Mitchell to investigate. Paul thinks it's a waste of time, but he soon finds himself saving the life of a woman - daughter of a war hero - who may be able to help him unlock the mystery of the ancient wreck.