When young inventor Bob Moore fails in his efforts to provide his father, a safe manufacturer, with a lock that is burglar proof, he contacts The "Eel," the most talented safecracker in the city, to offer him a job in his factory. The Eel, deciding to go straight, accepts the offer, but when he later learns that Irene Hardin has been given a valuable necklace by her father, The Eel plans one last job to secure Irene's pearls. Meanwhile, Irene's father, also a safe manufacturer, places the pearls in his own safe and tells Bob that if he can open it, Irene will be his. Bob, in love with Irene, opens the safe and places the pearls on the handle. After he departs, The Eel enters the house and steals the pearls. Bob is accused of the crime, and to exonerate himself, pursues The Eel. After a lively fight, Bob recovers the necklace and returns home to claim his bride.
Bob Moore worked night after night in the laboratory of his father's factory trying to invent a safe which could not be opened. For this reason he objects to having his father consolidate with John Hardin, who also makes safes. Bob says anyone can open Hardin's safe. Hardin tells Bob if he can open the safe in his library, he can have anything he has. Hardin urges his daughter, Irene, not to have anything further to do with young Moore. Irene, however, continues to call for Bob at the factory and Bob continues to call at the Hardin home, where he stays until he is put out. One night when Bob returns home he finds "The Eel," or John Rehan, who has the most sensitive fingers that ever twirled a safe knob, ransacking the safe which Bob has been telling himself cannot be opened. "The Eel," however, makes his getaway. Bob is determined to find the man again, for he realizes that he knows more about safes than he or his father, and with the help of a detective and his stool-pigeon, he finds "The Eel" at Molly Murta's apartment. "The Eel" has promised Molly to go straight. She loves him and is only glad when Bob offers "The Eel" a job at the factory. Hardin buys an expensive necklace for Irene's birthday gift. The purchase is witnessed by a henchman of The Eel." Irene wears the necklace to the factory, where both Bob and his helper see it. "The Eel" is tempted, but refrains. However, later, when the henchman tells him of the jewelry, "The Eel" determines to get the necklace. He is just beginning to open the safe, when Bob climbs through the window. He told Irene's father he can open his safe. "The Eel" watches Bob tamper with the safe. Finally it is opened, and hanging the necklace on the knob, the safe closed, Bob disappears through the window and telephones Irene to look on the knob of the safe for proof that he opened it. "The Eel" meanwhile has taken the jewel away, and Bob receives word that the necklace has disappeared. Bob, knowing that there is only one other man who could have opened the safe, starts for the café where "The Eel" and his bunch bang out. "The Eel" hurries to Molly to have her hide the necklace. Bob has just arrived at the café, where he finds "The Eel," and has demanded the necklace, when the police raid the place, and after a fight, Bob pulls "The Eel" out with him and they escape to Molly's flat. When the police knock at the door, Bob has already obtained the necklace and tells the officers that he came to see Mr. Rehan about some work. The police leave alter apologizing, and "The Eel consents to go back to work. Bob enters the Hardin home through the window and hands the necklace to Irene. Hardin is astonished and stammeringly tells the detectives that it was all just a little joke. They leave in disgust and Bob tells Hardin that, having opened the safe, he will now take the best he, Hardin, has. He puts his arms about Irene, Hardin is speechless; Moore, who is present, laughs uproariously. "Now go ahead with your consolidation," says Bob to the two fathers.
