The Gray Mask (1915)

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.