Police inspector Jim Garth, investigates the murder of Joe Kridel, another inspector, who had been tracking the Hennions, a gang of thieves plotting to steal the formula for a dangerous explosive from an old inventor. As Jim uncovers the Hennions' plans to procure the formula and sell it to an agent of an unfriendly foreign power, he encounters Nora, the former lover of Joe, who has sworn revenge for the killing and has ingratiated herself with the Hennions in order to discover the identity of the murderer. Although he assumes Nora is one of the thieves, Jim falls in love with her anyway, but she firmly rejects his advances. Disguised in a gray mask similar to the one worn by one of the gang members, Jim infiltrates the organization and foils the plot. With Joe's murderer in jail, a grateful Nora finally accepts Jim's affection.—Pamela Short

The Hennion gang of crooks having killed Joe Kridel, a police inspector, and fearing discovery, accept the aid of Simmons, who wears a gray mask that covers wounds caused by an explosion. Jim Garth, another inspector, is placed on the trail of the gang of which he becomes a member. Nora, the daughter of Garth's inspector, is beloved by Garth. She appears to be one of the gang. Although Jim loves her deeply, she is cold to him. She has sworn to avenge the murder of Kridel, and believes the murderer to be one of the gang. The Hennions attempt to steal a valuable explosive and penetrate to a steel room in which the chemical is placed. Nora learns the name of Kridel's murderer. When the gang has gathered in the steel room, Garth reveals himself and calls in the aid of the police. The gang is arrested; the murderer secured, and out of gratitude, Nora accepts Jim Garth as her lover.—Moving Picture World synopsis