Art Marvik, former Royal Marine Commando, is surprised by a late-night summons to meet Helen Shannon, a woman he helped on his first mission. Art Marvik, former Royal Marine Commando, is surprised to receive an unexpected summons to meet Helen Shannon, a woman he helped on his first mission, in the middle of the night. When a body is discovered in her flat, Marvik is convinced that Helen is being framed for murder, but why and by whom? Shortly afterwards, the head of the National Marine Intelligence Squad, Detective Chief Superintendent Crowder, asks him to investigate the disappearance of a salvage vessel, the Mary Jo, which went missing in 2003. As he delves into the past, it becomes clear that Marvik 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.