When Frank Stewart, a retired metallurgist, visits his old football pal Matt Morrison, Matt secures Frank a job at the Arlington Steel Mills where he himself is employed. Frank rents a room at Mrs. Morrison's boarding house, in which Matt, his sister Bebe, the gossipy old maid Elvira Appleby, Siggie Landers and the flirtatious Rita Martin and her jealous husband Dave live. The strain of manual labor prompts Frank to return to his experiments in metallurgy. On the night that he perfects his formula to remove impurities from steel, Rita visits him in his room, causing a fight between Dave and Frank. Rita relates Frank's success to her lover, George Barnes, a supervisor at the plant, who tells her to steal the formula. Following her lover's instructions, Rita again visits Frank in his room, where they are interrupted by Dave, who attacks Rita. To protect Rita, Frank knocks Dave unconscious, and while Frank carries Dave to his room, Rita steals the formula. When Miss Appleby gossips about Rita and Frank, Mrs. Morrison orders her out of the house and Dave follows her. Soon after, Frank discovers that his formula is missing and he decides to trail Rita. Dave also follows Rita to her meeting with Barnes, and when he surprises them, Barnes kills Dave. Because of the bad blood between Dave and Frank, Frank is arrested for murder, clearing the way for Barnes to sell his formula. Barnes gives the formula to Storm Swenson, the plant troublemaker, to sell at the rival Carleton steel mill. A short time later, Frank is released from jail for lack of evidence and begins to suspect that whoever stole the formula murdered Dave. As Frank and the others question Carleton, Barnes shoots Swenson down from a platform into a vat of molten steel. Convinced that Swenson was murdered, Frank warns Rita that her life is in danger and arranges a meeting with her. After substituting a dummy for Rita, Frank apprehends Barnes as he attempts to kill her. With the arrest of Rita and Barnes, Frank is exonerated of murder.
