

Speed and Trixie drive to the shipyard where the Masked Racer's car is being unloaded for the upcoming Trans Country Race. Trixie hints to Speed that he should enter the race. He hesitantly agrees. At the Racer homestead, while watching TV, Pops learns that Speed has entered the race. He "blows a gasket" and reminisces about the loss of his oldest son, Rex, who joined a race without his permission. At the brink of victory, Rex crashed the car Pops had built. Although Rex was uninjured, Pops refused to let him drive again, citing Rex's lack of experience. Consequently, Rex vowed never to return home. Meanwhile, the Alpha Team is holding a secret conference to plot a way to win the race. Mr. Wiley tells Mr. Fixer and Alpha Team driver Zoomer Slick to "pull the dirty trick first." Determined to beat the Masked Racer, Speed sneaks out in the middle of the night and goes to the track. Despite heavy rains he is not deterred. The Masked Racer warns him to stay out of the race.
After winning a practice race, Speed Racer is offered a position on a team set to race in the Grand Prix. The company who employs his father, Pops Racer, a top engineer, owns the team. However, Speed declines because Pops doesn't want him to become a pro. Meanwhile, Pops quits when his plans to improve the Mach 5 are rejected. While Pops and Speed are driving home, a gang of motorcycle racers steals their plans. Trixie, in her helicopter, runs the gang off the road and the plans are recovered. Back at the cyclist headquarters, bad guy Acey Ducey shows up and offers to get the plans for "5,000 clams." He confronts Pops but leaves empty-handed as Pops has hidden the designs on the Mach 5's windshield using invisible ink. Deciding to sell the Mach 5 so Pops can rebuild the engine, Speed visits Sparky, who suggests that Speed enter the Sword Mountain Race for a $5,000 prize. While Speed takes the Mach 5 out for a road test, "dirty driver" Duggery rams the car, causing it to blow a tire.
Speed resumes the Sword Mountain Race, neck and neck with Duggery. Ace and his gang approach from the opposite direction. Speed swerves off the road and uses his rotary saws to cut a path through the overgrown terrain. Trixie creates a temporary distraction, bombing the gang with smoke flares from her plane. At a cross-road, Duggery decides to take a "shortcut." Speed knows that the road leads to a dangerous volcano and sets out to rescue him. Meanwhile, Ace and his gang fire at Trixie. The plane plummets but Trixie escapes. At the edge of the volcano, Duggery is thrown from his car, and left dangling from a rock. Speed also ends up on a rock shelf after trying to rescue his competitor. They manage to reach safety but find that the gang surrounds the Mach 5, with Trixie taken hostage. Spritle and Chim Chim, who have hidden in the Mach 5's trunk, throw rocks at the gang while Speed, Duggery, and Trixie fight them off. Ace takes off in the Mach 5. Speed follows in hot pursuit.