In the year 1869, we follow the adventurous journey of Army Captain James West (Will Smith), who finds himself hiding in a railroad water tower to keep an eye on a group of ex-Confederate soldiers working under the notorious General "Bloodbath" McGrath (Ted Levine). As West tracks the soldiers to a lively saloon where General McGrath is caught up in the revelry, he witnesses the chaos caused by a large prostitute attempting to hypnotize the general into revealing his sinister plans.
Undeterred, West breaks into the establishment but is halted by the cunning prostitute, allowing McGrath to escape. After a fierce confrontation with McGrath's thugs, West discovers that the enigmatic figure is actually U.S. Marshal Artemus Gordon (Kevin Kline). The narrative quickly shifts to Washington, D.C., where West and Gordon are summoned to the White House by President Ulysses S. Grant (also portrayed by Kline). Grant informs them about the mysterious disappearances of key American scientists and tasks them with unraveling the mystery before the inauguration of the first transcontinental railroad at Promontory, Utah.
Their quest leads them to New Orleans, where they investigate a lead on Dr. Arliss Loveless (Kenneth Branagh), an ex-Confederate scientist who navigates his world in a steam-powered wheelchair after losing his legs. At one of Loveless's extravagant gatherings for Southern society's elite, West mistakenly identifies a female guest as Gordon in disguise, resulting in a predicament where the guests threaten to lynch him. In a parallel storyline, Gordon boldly explores the mansion, uncovering a caged damsel in distress, Rita Escobar (Salma Hayek), and courageously manages to rescue her.
Their escape from a dire situation is assisted by Gordon, who uses an elastic rope to free West from the clutches of an enraged mob. Once aboard The Wanderer, Rita appeals for their help to rescue her father, Professor Guillermo Escobar. As the plot thickens, Loveless showcases his latest weapon: a steam-powered tank, which he uses to mercilessly practice on General McGrath's men, inciting McGrath's wrath when he kills the general in cold blood, leaving him to die.
Upon discovering McGrath's fate, West reveals Loveless's dark history, that he previously orchestrated a massacre of free slaves, claiming West's own family lost their lives during that horrific event. In a race against time, West, Gordon, and Rita pursue Loveless, who has escaped on his armored train towards Utah. With thrilling ingenuity, West challenges Loveless's train while disabling it just moments before Loveless employs a cannon to halt The Wanderer. However, in a twist of fate, Rita accidentally releases sleeping gas, knocking out herself, West, and Gordon.
As the story unfolds, our heroes awaken only to find themselves enslaved by Loveless, who plans to abduct President Grant at the highly anticipated "golden spike" ceremony. In a moment of tension, West and Gordon employ a clever strategy to evade lethal flying disks activated by their collars. By timing a leap into a pit of mud, they foil the deadly trap, and soon they stumble upon Loveless's private railroad that leads to his nefarious operations. Here, they are introduced to Loveless's ultimate weapon—a gargantuan mechanical spider equipped with advanced weaponry.
As Loveless sets his dastardly plan in motion at the inauguration ceremony, capturing both Gordon and Grant, West appears to be eliminated by one of Loveless's henchmen. However, in a surprising turn of events, it’s revealed that West used a cleverly disguised layer of chain mail to survive. Dressed as a belly dancer, he distracts Loveless with a captivating performance, all while plotting to rescue his comrades.
Inspired by the fierce spirit of desert creatures, West and Gordon craft a flying machine to engage Loveless’s formidable spider. In a perilous confrontation aboard the spider, West proves his mettle against the crew adorned with peculiar prosthetics. Eventually, Loveless himself engages in a showdown with West, but is taken down when Gordon destroys his wicked mechanical apparatus.
In a gripping finale, Loveless, now wielding advanced hydraulic legs, attempts to take down West but meets his demise when West releases a lever, sending him plummeting into a canyon as the spider careens out of control. After the dust settles at Promontory, President Grant recognizes West and Gordon's bravery, promoting them to the inaugural agents of the U.S. Secret Service. In a humorous twist, as they prepare to woo Rita, she surprises both men with the revelation that Professor Escobar is her husband, shattering their aspirations. The adventure concludes with West and Gordon adventurously riding Loveless’s steam-spider as they journey into the sunset.
