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Assigned to work at the Jupiter Powder Plant to develop a secret explosive, befuddled young scientist J. Quincy Pennant rents a room at Mrs. Douglas' boardinghouse, where he meets his fellow boarders Dolly Smythe, Sue, Betty and Helen, who are employed as dancers at the Rainbow Gardens casino. Pennant is "adopted' by the glamorous foursome when he evicts Dolly's boisterous suitor, Jeems O'Shea, from the house. Reporting for work at the plant, Pennant meets Dr. Wayne, the head of operations, and his assistant, Oliver Lindsay. Lindsay, who in reality is an enemy agent, becomes annoyed when Pennant refuses to keep a journal of his work. To keep track of Pennant, Wayne assigns Jeems, a plant employee. At first angry with Pennant for humiliating him in front of Dolly, Jeems soon grows to respect the scientist's nerve of steel, and the two become friends. After working continuously for three days and nights, Pennant develops an explosive that can skip over long distances, and Wayne insists that the scientist transcribe his formula. That night, Pennant returns to the boardinghouse with a gift for his neighbor, Sally Dean, with whom he is smitten. When Sally rejects his gift, Pennant laments that he lacks a "formula for love," and the other girls comfort him. After the plant vault is robbed of everything except Pennant's notes, which are in code, Wayne orders the scientist to carry his code in a gunbelt and assigns Jeems to protect him. Unsuccessful at stealing Pennant's plans, Lindsay sends for Sally and offers her money to win the scientist's confidence and formula. Sally accepts his offer and when Pennant professes his love but refuses to decipher his code, she snubs him. When the other girls discover Pennant's coded worksheets, they assume that he is a professional gambler and invite him to the casino that night. Meanwhile, an impatient Lindsay orders Harvey Dodge, his accomplice, to use force to obtain the code. Dodge follows Pennant to the casino, where he attempts to drug the scientist's drink. When Meeker, Jeem's friend, drinks the drugged potion instead, Pennant takes to the gambling tables and wins all the jackpots. Dodge's thugs then stage a fight in which they knock Pennant unconscious and steal the belt containing his notes. Sally and the girls carry the dazed scientist to the office of Chick Parker, owner of the club and also an espionage agent. There, after returning Pennant's notes, Sally locks the door against Dodge's thugs and escapes out the back door with the scientist. At the plant the next day, Wayne chides Pennant for his irresponsible behavior, and the scientist promises to complete his formula by Thursday for a test run. Meanwhile, Lindsay, believing that Sally is now in possession of the formula, offers her fifty dollars for it. On the day of the test, Lindsay's thugs knock Jeems unconscious as he loads explosives in the powder magazine, and when his friend fails to appear at the test site, Pennant goes to look for him. Back at the boardinghouse, Dolly confronts Sally about her duplicity, and the two decide to join forces and save Pennant. Meanwhile, Douglas' thugs have captured Pennant and, after planting a time bomb in the powder magazine, tie him up next to Jeems. Rushing to the plant, Dolly and Sally accuse Lindsay of espionage. In response, he draws a gun and drives away with his accomplices. Discovering that Pennant is still missing, Wayne and the women rush to the powder magazine, where they free the two men. When Jeems warns that a time bomb is about to explode, he and Pennant load the bomb onto a cart and speed down the road away from the plant, where they intercept Lindsay's getaway car. Lindsay tries to run the cart off the road, but only succeeds in knocking Jeems and Pennant off the cart and into a pond. At that moment, the bomb detonates, blowing up Lindsay and his gang. Back at plant headquarters, Wayne demands the formula, and after giving it to him, the scientist declares that he has finally found his "love formula" and kisses Sally.