'Schwerttrager!' Commander David Cochrane Smith listens to the dying words of a U-boat commander: 'Sword-bearer'. It is the summer of 1917 and Britain is losing battle against the U-boats. Smith is convinced that Schwerttrager is the code name for an operation that threatens Britain. Nobody will listen to him. Mistrusted by the Admiralty, Smith is given a flotilla of two inadequate boats backed up by a feeble 'ship of force' to fight off the mighty U-boat threat. Not only does Smith have to face the greater sophistication of enemy destroyers, but he finds himself in conflict with his commanding officer. His plight worsens when he becomes immersed in the terrifying world of espionage behind enemy lines. But through it all, the enigma behind the Schwerttrager lures him on, until he risks his career and his life in a desperate last-ditch attempt to solve the mystery.