1805-The British man-of-war H.M.S. Vanguard disappears mysteriously with all hands in a fiery explosion, returning to Portsmouth Harbor after the harrowing Battle of Trafalgar. For nearly two centuries, the warship's loss proves an unexplained riddle for maritime historians and scholars. "Was it an accident or the treachery of French spies?" The answer has lain hidden in the cold silence of the deep waters and silt burying the Vanguard between Portsmouth and the Isle of Wight, but a large iron box and a journal recovered in a crafted watertight container hold the answers. The crew of the American oceanographic and salvage ship, the SS Reprise, locate and recover the stern of the Vanguard. Alan Ward, the operator of the Reprise's unmanned submersibles, stumbles upon the frightening truth and the horror that engulfed the Vanguard's crew as they fell victim to a deadly siren, a "vampiresa," a female vampire, plaguing their vessel.