Undercover investigator Art Marvik faces a desperate battle to save others from a ruthless assassin who will stop at nothing in order to protect the secret of the Mary Jo's last voyage from ever being exposed. Former Royal Marine Commando, now undercover investigator for the UK Police National Intelligence Marine Squad is surprised to receive an unexpected summons from Helen Shannon, a woman he helped on his first mission for the squad. When a body is discovered in her flat, Marvik is convinced that Helen is being framed for murder, but why and by whom? Before he has a chance to follow it up, the head of the Squad, Detective Chief Superintendent Crowder, asks Marvik to investigate the disappearance of a salvage vessel, the Mary Jo, which went missing in 2003. As Marvik delves into the past, it becomes clear that he faces a desperate battle to keep Helen and others safe from a ruthless assassin - one who will stop at nothing in order to protect the secret of the Mary Jo's last voyage from ever being exposed.