In 1914 in East Africa, English nobleman Sir Everard Dominey, who abandoned his wife and home, is rescued from the jungle by Baron Leopold von Ragostein, a former classmate and his exact lookalike.  Dominey, who had been lion hunting, was abandoned by his crew and collapsed due to exhaustion and alcoholism.

Austrian Leopold has been working for German Sir Ivan Brunn, a munitions manufacturer, who has been infiltrating war departments around Europe to instigate war, and who also is plotting to destroy England's munitions factories when the war erupts.  Leopold, who was banished from Austria for killing his lover Princess Stephanie's husband in a duel, plots with Dr. Treak to have Dominey killed, while he impersonates him and returns to England to work for Brunn's cause.

Unknown even to Dr. Treak, Dominey overhears their plans and kills Leopold, returning to England as Leopold impersonating himself.  Dominey is assisted by Seaman, Brunn's right hand man and, at his estate, discovers his wife Eleanor has gone temporarily insane because she believes he killed the housekeeper Mrs. Unthank's son on their wedding night and left his body in the infamous Black Bog.

Thoroughly reformed, Dominey restores Eleanor's faith in him and his family name, and fends off the advances of Stephanie, who believes he is Leopold.  Dominey flushes out Mrs. Unthank's son, who is actually alive and, because of his insanity, has been terrorizing Eleanor.  Mrs. Unthank shoots her own son to save him from certain misery at the hands of mental institutions.  Dominey goes along with Brunn's plans and has operatives and a special radio installed in the attic of his home.

War is declared, and Seaman succeeds in his plans, but before he leaves for Europe, Stephanie brings Dr. Treak to the estate and he reveals Dominey.  Dominey overcomes Seaman and shoots out the radio, then becomes a national hero for exposing the munitions plot.  While recovering from a gunshot wound received during his chase after Seaman, Dominey is commended by the king and reunites with his wife.