"O'Malley of the Mounted" is a sergeant who has won his stripes by getting any criminal he is sent out to arrest, this in wild Northwestern territory amid men who dare follow their own impulses rather than obey the law.[3]
O'Malley is assigned to arrest La Grange, a man who murdered a saloon keeper. O'Malley believes La Grange went south to escape over the border into America.[3]
He encounters outlaws at a saloon in Forker City. He joins their gang by robbing a bank of $5,000.[3]
He soon develops a crush on Rose Lanier and a friendship with her brother, Bud, a fugitive of the law.[3]
Later, O'Malley fights a character named Red Jaeger who later exposes O'Malley as a Mountie and traitor. O'Malley is bound to a tree as the criminals plan to execute him at daybreak via hanging. Rose Lanier pretends to be against him, but clandestinely hands him a knife to rescue him.[3]
According to Motion Picture World, the film concludes:
By Rose and Bud the sergeant is rescued from sure death. While riding with them toward the border he confirms his suspicions that Bud is the murderer he is seeking, but finds that the killing was done to avenge a wronged sister. He leaves the brother and sister to make his report, and finds his act justified by his commanding officer. He returns to his loved one no longer "O'Malley of the Mounted."[3]
A 1921 lobby card depicting a scene from the film; William S. Hart's character tells Bert Sprotte's character, "I'm going to resign from the service -- I can't arrest the brother of the woman I love."