Detroit engineer Preston Tucker has been interested in building cars since childhood. During World War II he designed an armored car for the military and made money building gun turrets for aircraft in a small shop next to his home in Ypsilanti, Michigan. As the war winds down, Tucker becomes inspired to build the "car of the future". The "Tucker Torpedo" will feature revolutionary safety designs, including disc brakes, seat belts, a pop-out windshield, and headlights which swivel when you turn. Tucker hires young designer Alex Tremulis to help with the design and enlists New York financier Abe Karatz to arrange financial support. Raising the money through a stock issue, Tucker and Karatz acquire the enormous Dodge Chicago Plant to begin manufacturing. Abe hires Robert Bennington to run the new Tucker Corporation on a day-to-day basis.
Launching "the car of tomorrow" in a spectacular way, the Tucker Corporation is met with enthusiasm from shareholders and the general public. However, the Tucker company board of directors, unsure of his ability to overcome the technical and financial obstacles ahead, send Tucker off on a publicity campaign and attempt to take complete control of the company. While Tucker travels the country, Bennington and directors change the design of Tucker's car to a more conventional design, eliminating the safety and engineering advances Tucker was advertising. At the same time, Tucker faces animosity from the Big Three automakers -- General Motors, Ford and Chrysler—and from the authorities, led by Michigan Senator Homer S. Ferguson.
Tucker returns from his publicity tour and confronts Bennington, who curtly informs him that he no longer has any power in the company to make decisions, that the engine originally planned for the car is not viable. Tucker then receives a call from Howard Hughes, who sends a private plane to bring Tucker to his aircraft manufacturing site. Hughes advises Tucker to purchase the Aircooled Motors Company, which can supply both the steel Tucker needs, as well as a small, powerful helicopter engine that might replace Tucker's original "589" power plant.
Unable to change Bennington's design, Tucker modifies the new engine. He installs it in a test Tucker, in the secrecy of his backyard tool-and-die shop. This prototype proves successful, both in durability and in crash-testing. However, Tucker is confronted with allegations of stock fraud. Ferguson's investigation with the U.S. Securities and Exchange Commission (SEC) causes Karatz—once convicted of bank fraud—to resign out of fear that his criminal record will prejudice the hearings. Yellow journalism all but ruins Tucker's public image; yet the ultimate courtroom battle is resolved when he parades his entire production run of 50 Tucker Torpedoes, proving that he has reached production status.
After giving a speech to the jurors on how capitalism in the United States is harmed by efforts of large corporations against small entrepreneurs like himself, Tucker is acquitted on all charges, although his company falls into bankruptcy. In the film's closing shot, Tucker's entire production line—fifty "cars of the future"—is driven through the streets of downtown Chicago, admired by everyone as they pass.
