Financial tycoon John Taney is at home working in his study when Jim and Artie shove past his butler barge in. As the clock strikes one, the agents tell Taney to get everyone out of the house. He refuses, drawing a derringer on them, and the teacup on his desk starts rattling. The room starts to shake and windows shatter, and Jim and Artie go to the window. Outside, a giant tuning fork mounted on a black wagon is pointed at the house. Artie gets Taney and the staff out while Jim goes after wagon. Two thugs drop down on him from a tree and he takes them out, but the wagon driver aims the tuning fork at the agent, knocking him unconscious.
When Jim wakes up, he finds himself on the Wanderer with an attractive woman hovering over him. Artie introduces her as Arden Masterson, Colonel Richmond's new assistant. General Caswell, Head of Army Ordinance Development, is also present and eager to find out what destroyed Taney's home as well as several other tycoons in the last week. Artie leads them to the lab car and uses a tuning fork to demonstrate that he can destroy a crystal glass from a short distance. Caswell wants them to find the weapon and offers to put men at their disposal, but the agents prefer to work on their own and avoid scaring off their quarry. Artie shows them a letter from the Cyclops Insurance Company that he found at Taney's house, trying to sell him insurance. However, the company is only a month old and so far no one has bought insurance from them. Artie heads for the Midas Club to meet with Taney and the other tycoon s while Jim checks out the insurance company.
At the Midas Club, millionaire Asa Dempster greets Artie and takes him to the boardroom. Taney and his cohorts are playing poker and they all admit that Cyclops approached them with an insurance offer. The ones who refused had their homes destroyed. Artie wants the tycoons to help the Secret Service set a trap, but Taney refuses, pointing out that the agents can't guarantee their safety. When Artie warns that the extortionists will never stop demanding more money, Dempster says that they can afford the loss. If the Secret Service fails to capture the people responsible then the tycoons won't have to pay anything. A disgusted Artie leaves, warning them that they may not be as safe as they think.
Jim goes to Cyclops Insurance and talks to the secretary, Cora Lister. She apologizes and explains that her boss, Mr. Singleton, won't see anyone. She calls him over the speaker tube but he tells Singleton to send any visitor away. When Jim tries to go in, the clerks reveal that they are thugs working for Singleton. Jim makes a graceful exit but then climbs out the window and enters Singleton's office. There is no one there and Jim looks around, unaware that someone is watching him through a peephole. Jim finds some fortune-telling weight cards in the otherwise empty desk, and then locates a gramophone set to play a pre-recorded message when Cora calls in. Three of Singleton's men come in and one of them shoots at Jim, who blocks the bullet with a ledger. He knocks the men out and then leaves with the gramophone.
Back at the train, Artie listens to the gramophone voice and identifies it as belong to Dr. Tebor Kovacs, an acoustic expert who went to jail for selling government secrets. He was released a year ago and weighed 284 pounds at the time. One of the weight cards says 284 and Artie figures that fat men tend to collect their cards. Jim takes off with the weight cards to find a matching machine while Artie discovers a French menu inside the gramophone. He takes Arden with him to meet with a French chef, Marcel, that he knows. Marcel explains that there is no restaurant in the U.S. that could produce such high-cuisine. However, Marcel says that the Epicurean Society might have such a menu. However, new members are only accepted by vote. As they go, Arden wonders how Artie would recognize Kovacs if he got in, but the agent figures that spotting a 284-pound man won't be difficult.
Jim checks fortunetelling weight machines across the city and ends up at an arcade. The cashier, Billie, wonders what he's doing and Jim explains that he collects weight cards. Billie hasn't seen the particular cards that Jim has but suggests he check out an arcade supply warehouse. As Jim leaves, a repairman from the warehouse overhears the conversation.
Artie enters the Epicurean Society, posing as Salvatore, an Italian waiter. The maitre d'hôtel refuses to tell Artie their names, saying that the members have no interested in being greeted by the waiters. The five members, four men and a woman, arrive but Artie realizes that they are all overweight. He serves dinner and disdains the food, and the woman, Miss Litefoot, asks him to explain. While Artie starts to describe the poor quality of the good, a man named Durkin strolls in. He apologizes for being late, pours himself a drink, and tells everyone to eat up. He then asks for ketchup with his meal and starts guzzling his food, and the maitre d'hôtel tells Artie that Durkin is a guest of one of the absent regular members.
Jim breaks into the warehouse and finds the right machine, but Singletons speaks through it, telling Jim to have a free fortune. The gypsy fortuneteller dummy inside hands out a fortune, which says to beware of unfriendly cyclops. Singleton's men attack the agent and he disposes of them, but inadvertently stumbles and grabs a grip-measuring machine. The handle electrifies and the current locks Jim's grip. The machine swings around on a platform, revealing a shooting gallery on the other side.
Artie carves a toothpick for Durkin, figuring he'll need it. Durkin is unimpressed with the food, except for the ketchup, and takes the toothpick from Artie. He tells the maitre d'hôtel that the food is terrible and they'll be out of business in a month, and then leaves. Artie tells the maitre d'hôtel he'd never work at such a crude place and leaves, following Durkin.
When Jim wakes up, he discovers that he's been tied to a post in the shooting gallery. Taney comes in with his thugs and Jim realizes that he's Kovacs, and lost the weight in prison. Once he got out, Kovacs set up a new identified. The thugs start firing at the gallery targets around Jim while Taney points out the tuning fork wagon nearby. He explains that he uses the warehouse as a cover for his real business, and has taken the money he obtained by extortion and used it to build an even larger tuning fork. Once it is completed, he can sell it to foreign powers who will use it to attack their enemies and the United States, vaporizing fortifications and fixed weapons.
A signal bell rings and Durkin comes in. Kovacs sent him to try the food since he couldn't risk being scene, but Durkin dismisses it as mediocre. Disgusted at Durkin's unrefined palate, Kovacs gives him a gun and tells him to kill Jim. However, as Durkin prepares to fire, the bell rings again. Artie comes in, disguised as an elderly gas inspector. While everyone is watching Artie, Jim starts cutting his ropes on a spinning gallery wheel. Artie feigns being near-sighted, mistaking Jim for a dummy, and offers to take a few shots at the gallery targets. Glad to let him, the thugs give Artie a gun and he fires wildly. Jim breaks free and the two agents take out the thugs. Artie tries to shut down the tuning fork but Durkin attacks him and they bump into the control. The tuning fork activates, shaking apart the room, and Jim and Artie get out. An armed Kovacs is waiting for them in the next room but the agents drop a crate on him. The fortunetelling machine activates again, giving Kovacs a fortune saying he's going on a long journey.
Later, Jim and Artie bring their dates to the Wanderer. Jim is eager to show off his partner's tuning forks but neither he nor Artie can get them to shatter a glass. As they leave, one of the women picks up the tuning fork, hits it, and breaks ever beaker in Artie's lab.