Lily is performing at the Birdcage when she sees a handsome man in a white suit casually twirling three walnut shells. She goes over to the man and figures that he's a thimblerigger. The man concedes that he is but assures her that he's not there to gamble or con anyone. He simply enjoys playing the game, but warns Lily that he's there to destroy a man.
The next day, Lily stops by the marshal's office, where Johnny is telling Dan about the virtues of the local men's Glee Club, where they spend their time playing poker. Johnny says that only bachelors are allowed and eyes Lily as she comes in and says that Dan probably couldn't play. He slips out as Lily overhears the conversation and suggests that Dan is suffering from bacheloritis. She says that she knows a cure but Dan tells her to get down to business. Lily explains about the Thimblerigger and how he's promised to destroy a man.
Dan goes to the Birdcage and sits down opposite the Thimblerigger, who is still gently twirling his walnut shells between his fingers. When Dan says that he wants to know how the man plans to kill a man, the Thimblerigger explains that he's there to destroy a man, not kill him. As a crowd gathers, the Thimblerigger describes how a man and his young wife in Louisiana were riding through the countryside on their honeymoon. Three highwaymen came upon them and the groom begged them to spare his life, offering up his wife. Disgusted, the head outlaw ordered the husband away. The wife was never seen and the husband lied about what happened and claimed that he fought but was overpowered. However, when one of the bandits was captured, he testified and the community realized the truth of what had happened. The husband fled in the night, changed his name, and disappeared.
The Thimblerigger tells Dan that he's there because the husband may be in Laramie. A local man, Ed Shafter, steps forward and says that a man like that ought to be hung. Dan invites the Thimblerigger to point the man out, but the Thimblerigger says that there's no law against cowardice and no one could do anything. The husband fears exposure and would just move on if he were revealed for what he was. The Thimblerigger admits that the husband doesn't know who the Thimblerigger is and will suffer from the guilt and the suspicion, just like the wife suffered before she died. Eventually the man will pick a shell and get the pea, and the Thimblerigger will know who he is and so will everyone else.
Dan thinks the whole thing sounds strange, but the Thimblerigger says that the retribution he seeks is within the law. Ed steps forward and offers to pick a shell. He's confident there will be nothing under it and says that the bandits would have had to kill him to get to the woman. Ed threatens to shoot the Thimblerigger if there's a pea under the shell he picks, but the Thimblerigger simply says that he'll take his chances. When Ed picks a shell, there's no pea under it and he offers a drink to every man in the saloon who picks a shell. As Ed goes to the bar, he invites a local, Sam White, to join the line. Sam says that the line is too long and he has to leave, and Ed looks suspiciously after him.
Dan visits the bar later and Lily tells him what has happened. Ed has forced every man to pick a shell for fear that they'll be judged guilty if they don't. Dan warns that the Thimblerigger will move onto another saloon and Lily asks him to find the man that the Thimblerigger is looking for. As Dan goes out, Ed says that they have a group of regulators ready to deal with the husband when they find him. Dan orders them all to turn in their guns and leaves, but Ed removes a lynching rope from beneath his jacket.
That night, Dan and Johnny hear Sam on the street. Some of Johnny's Glee Club friends are there, confronting Sam. They invite him to join them in the Birdcage for a drink but Sam refuses and Dan orders them off. He takes Sam into the marshal's office and tells him that he'll protect him no matter what, and no one will make Sam do something he doesn't want to do. Sam snaps at him, complaining that Dan is picking on him by offering to protect him. He figures that Dan realizes that he's the husband and is in league with the Thimblerigger, but Dan simply insists that Sam can go anytime he wants. Sam accuses Dan of telling him to run but the marshal simply repeats his statement and suggests that he get some rest.
Johnny is at the saloon later with the others when Sam enters. Everyone in the room looks at him suspiciously and after a moment, Sam walks over to the Thimblerigger's table. Johnny goes to get Dan and they return to the Birdcage. Sam tells them to stay out of it, reminding Dan that he promised to protect him. He figures that he has more of a chance with the Thimblerigger then he does with Ed. Dan orders Ed to drop the noose but Sam reaches forward and chooses a shell. The Thimblerigger flips it over and a pea rolls out, dropping to Sam's feet.
Sam wonders who the man is and the Thimblerigger says that he was the highwayman that Sam gave his wife to. Disgusted, Sam dismisses him as a common thief, draws a gun, and shoots the Thimblerigger in the side. Dan disarms Sam and orders everyone out, and Johnny takes Sam to jail. The marshal examines the wound and realizes that it's fatal, and the Thimblerigger tells him that the wife stayed with him. However, she never stopped loving Sam until the day she died even though he was a coward. The Thimblerigger hated him because she never gave up on Sam, but he didn't get a good look at Sam's face. All he saw was the look of terror, and he knew Sam could never conceal it. The Thimblerigger has been playing the game for six years and Sam was the first one he saw who had the look.
Dying, the Thimblerigger flips over the other two shells, revealing peas beneath them. Dan wonders why Sam came in and Lily figures that Sam wanted to prove he was innocent even when he knew he was guilty. The marshal figures that Sam did have a chance... on the road when the highwaymen confronted him.