A British battleship mysteriously explodes at anchor inside a heavily defended home port at the start of World War II. MI-5 Officer Richard Kast uncovers troubling evidence of espionage but superiors whitewash the investigation.
Additional incidents follow, instigated by an elusive stranger who leaves subtle clues to taunt Kast and test his mettle. As London burns from nightly bombing raids, the pursuit becomes an intense psychological duel between a steadfast but burdened ex-boxer's stubborn resolve and the street-wise mischief and guile of a master German spy. At stake, disclosure of illegal aid agreements which threaten America's entry into the war and possession of a secret radar device which will end the bombs.
Similar societal outcasts, one man seeks redemption and the other retribution. Neither knows or expects quarter.