As the Silver Streak made its way toward Chicago, book editor George Caldwell found himself amidst a serendipitous encounter that would ultimately change his life forever. While enjoying the luxuries of the train's carriage, he struck up a conversation with salesman Bob Sweet and Hilly Burns, the intriguing secretary to the well-known Rembrandt scholar, Professor Schreiner. Sparks ignited as George and Hilly felt an immediate connection, leading to her inviting him to her cozy cabin. It was there that he witnessed the shocking sight of Schreiner's body tumbling from the train's rooftop, a gruesome event that left George rattled, though Hilly remained disbelieving.
Determined to uncover the truth, George initiated his own investigation, stumbling upon Whiney and Reace rifling through Schreiner's possessions, their intentions clearly nefarious. After a perilous confrontation where Reace violently threw George off the train, he was forced to trek through dangerous terrain on foot.
Fate intervened when he encountered a cunning farmer who whisked him away in her biplane, enabling him to reboard the Silver Streak at a station ahead of its course. However, George's concern for Hilly's safety grew when he saw her with art dealer Roger Devereau, leading him to suspect a romantic affair. Convinced he had misunderstood, George confronted Devereau, who clarified that Wiley and Reace were simply his henchmen and that Schreiner’s supposed death was merely a facade. Devereau then introduced George to a revitalized Schreiner—more accurately, Johnson, another of his employees posing as the professor.
Devastated by what he thought was Hilly’s betrayal, George succumbed to despair, confiding in Sweet, who then revealed his true identity as Stevens, an undercover FBI agent. As George recounted his misfortunes, Stevens explained that Devereau was a cutthroat criminal posing as a legitimate art appraiser who was actually seeking Schreiner's Rembrandt letters—documents that could incriminate him for authenticating forgeries as genuine works. A light finally dawned on George regarding the significance of the hidden letters tucked away in Schreiner's book. He quickly shared this critical information with Stevens, only for their discussion to be cut short by Reace, who attempted to kill George but ultimately ended Stevens’ life instead.
A desperate chase ensued as George confronted Reace on the train’s rooftop, skillfully eliminating him with a harpoon gun that sent him plummeting to his end. Picking up the pieces once again, George found himself on foot, endeavoring to navigate through a hostile landscape while facing the disbelief of the local sheriff who dismissed his incredible tale. As the authorities pursued him for Stevens' murder, George made a daring escape, unaware of the relentless car thief Grover T. Muldoon, who was hot on his trail. Together, they orchestrated a plan to catch up with the Silver Streak in Kansas City, bolstered by George’s unyielding resolve to rescue Hilly from Devereau’s grasp.
As the hunt for George escalated, Grover resorted to cunning trickery, disguising George as a black man using shoe polish. This clever ruse allowed them to reboard the train incognito. Meanwhile, Devereau regained control of the situation, seizing the Rembrandt letters and igniting a plan to burn them to ashes. He revealed his intention to frame George and Hilly for Schreiner's murder, concocting a deadly double-murder-suicide plot.
Disguised as a train steward, Grover ingeniously orchestrated a rescue for George and Hilly, yet their brief respite led them to leap from the train amid a chaotic gunfight against Devereau’s henchmen. The authorities quickly apprehended them, bringing them before Chief Donaldson, who was unwavering in his belief in George's innocence. He disclosed that the FBI had intentionally spread false news, creating a diversion that led Devereau to assume George was guilty while ensuring his safety.
After amicably parting ways with Grover, Donaldson ordered the train to be halted and surrounded by police forces. A fierce firefight erupted, injuring Whiney. In a race against time, George and Grover quickly reunited in their quest to breach the train and rescue Hilly from Devereau’s clutches. The villain, however, had taken control of the train and was playing with fire by setting it on a collision course while disposing of Whiney from the train. With Donaldson offering aerial support from a helicopter, George delivered the final strike to Devereau, whose life was abruptly ended by the unforgiving force of an oncoming freight train.
In the aftermath, as the runaway Silver Streak careened toward disaster, George teamed up with a porter to disengage the train cars from the engine, triggering the brakes just in time to save the remaining passengers. However, despite their efforts, the train’s momentum proved too great, culminating in a catastrophic crash at Chicago's Central Station, leaving devastation in its wake. As Grover made his getaway in a stolen vehicle, George and Hilly exchanged heartfelt farewells, stepping forward into a new chapter of their lives amidst the ruins of the city.
