Traveling under the name "Charles Conant," the son of an American mine owner tries to enter England in 1916 after masquerading as a muleteer, but the captain of his ship, suspicious when he sees him looking through a spyglass, plans to take him back to the United States. Charles escapes and visits his relative, Lady Dartridge, and falls in love with her daughter, Lady Joan Templar, who is loved by her cousin, chief constable George Templar who, suspicious of Charles' manner and unexplainable meetings and activities, wants to arrest him as a spy. After Charles handcuffs two German agents, he reveals that he is a secret-service man. Earlier, he mistakenly sold titanium from his father's mine to a German agent. His successful mission recovered the titanium before it went to Germany aboard a U-boat. Promising to wed Lady Joan, Charles leaves to join the Lafayette Squadron in France.