In Denver, an organ grinder and his monkey entertain children outside the building of the Jupiter Corporation when Jim rides into town. Jim demands entrance and heads upstairs to the meeting room. The board is waiting for their missing member when Jim comes in and notices the monkey has an explosive. Jim grabs and throws it into a closet where it explodes harmlessly while the monkey makes its escape.
The board members are cleaning up when Amelia Branston, the acting chairman, arrives with her assistant Kyra. Her late arrival looks suspicious, and Jim notes that two other board members have died in seeming accidents, and the President received a letter hinting they were murdered. Since the Jupiter Corporation is a major defense company, the government is interested. Jim asks for a free hand to assure security for the board and Amelia makes a motion to accept. The board votes unanimously to accept... but Amelia overrides them.
Later Jim secretly meets with one of the board members, Gorhan, who he's identified as the man who sent the letter. Gorhan reveals the dead men were involved with a scheme to dump their stocks and cause a panic. They wanted to get Gorhan involved but he refused, and knows who was involved. Jim is distracted by a woman long enough for Gorhan to be taken outside by someone and killed. Jim fights Gorhan's killers but is knocked out and they make their escape.
Later Jim goes to see Amelia but is turned away at the door by her menservants. Undeterred, Jim climbs up to the second floor and finds Kyra playing a lute. After a few minutes of her singing, he interrupted as Amelia arrives and tells her about Gorhan's death. Amelia talks about her brother Simon who founded the Jupiter Corporation but was hounded into a heart attack. Amelia refuses to help the board members but they're interrupted when two boxers barge into the room. The main fighter, Lionel, disposes of his opponent but Jim is unimpressed, having noted he has weighted gloves. Lionel is Simon's son, Amelia's nephew, and takes offense at Jim's accusation. Jim easily disposes of him and leaves, warning Amelia that Simon was murdered.
At the Wanderer, Amelia and Lionel arrive and Lionel demands to know what Jim meant. Jim doesn't have anything to confirm his suspicion... yet, and Lionel agrees to stay out of his way, but will come after him once the case is solved. Amelia invites Jim to the corporation meeting the next day. At the meeting, Amelia moves that Jim be made acting chairman to act as security for the board, and refuses to vote to approve his involvement otherwise. The board caves to her and she assigns Lionel to Jim as his assistant. Lionel is not enthusiastic about the idea but goes along and explains what a dump-and-panic scheme is, and how someone can get control of the company. He suggests they contact the brokers and Jim tells him to do it. When Lionel insists Jim make him do so, Jim goes ahead.
Late Kyra meets with Lionel as he goes through the papers and it's clear they're romantically involved. Lionel interrupts the kiss when he finds the address the schemers are using. Lionel pays a visit to the address where a circus-themed bar is located. He doesn't have any luck asking after the fake names of the schemers except for one who is in the back room. Lionel goes to meet with the man but finds several thugs waiting for him.
Jim is going over Lionel's papers but the address for the bar isn't there. He gets the address from Kyra and goes there where the bartender says he hasn't seen Lionel. Jim does find one of Lionel's distinctive cigars and the bartender offers to check with the late shift. Jim takes a seat to wait and watches the seal show, but is attacked by jugglers. When Jim tries to follow the man back stage, the clowns attack him. Jim takes them out and goes backstage to find Lionel tied up and gagged. After freeing him, they find a mock-up of the board room with mannequins for the board members. Lionel finds a wooden model of a Gatling gun but they're unaware that several of the mannequins are men in disguise.
Jim and Lionel are knocked out from behind and tied to the chairs around the fake table. Someone has tied them to a crossbow bolt with a candle burning through the rope and they have five minutes left. Jim uses an acid pellet from his boot heel to start freeing the chairs from the floor, while figuring the Gatling gun in the real board room is authentic. The board members arrive at the meeting room to find a (fake) note from Jim asking them to wait.
Jim and Lionel manage to break the chairs free just in time and get to the Jupiter Corporation board room in time to get everyone down as the Gatling gun goes off. Amelia and Kyra then come in and Amelia reveals she was responsible. She takes Kyra hostage and reveals she killed Simon when he refused to go along with her dump-and-panic scheme. Amelia has now bought all of the shares to take control of the corporation. Kyra pleads for Lionel's life but Amelia tosses her off and prepares to throw a mercury-phosphate grenade. She calls for the elevator but is unaware that the cage has kept going up past the floor. She ignores Jim's "look behind you" warning and she falls to her death.
Later at the Wanderer, Jim is dictating a report to an assistant while waiting for Lionel to arrive. Lionel insists on having their little talk' and thanks him for being made chairman of the board. He announces that he and Kyra are getting married and Jim invites them in for dinner. He sends Kyra back to the kitchen to prepare supper while he and Lionel share a toast.