THE ADVENTURES OF BUCKAROO BANZAI ACROSS THE 8TH DIMENSION

Buckaroo Banzai and his mentor Dr. Tohichi Hikita perfect the "oscillation overthruster", a device that allows an object to pass through solid matter. Banzai tests it by driving his Jet Car through a mountain. While in transit, he finds himself in another dimension. After exiting the mountain and returning to his normal dimension, he discovers an alien organism has attached itself to his car.

Dr. Emilio Lizardo, incarcerated at the Trenton Home for the Criminally Insane, sees a television news story of Banzai's successful test. In 1938, Drs. Lizardo and Hikita had built a prototype overthruster in Princeton, New Jersey, but he tested it before it was ready and became stuck between dimensions. In those moments, he saw alien creatures and struggled until freed by his colleagues, emerging crazily changed and violent. Understanding that Banzai has finally accessed the 8th dimension, Lizardo escapes the asylum and plots to steal the overthruster.

Banzai and his band, "The Hong Kong Cavaliers", are performing at a nightclub when Banzai interrupts their musical intro to speak to a sad woman in the audience, Penny Priddy. During a song he performs especially for her ("Since I Don't Have You"), she attempts to shoot herself, which is mistaken for an assassination attempt on Banzai. After questioning her at the New Brunswick jail, he realizes she is his late wife Peggy's long-lost identical twin sister and bails her out.

Later, during a press conference to discuss his Jet Car experience, the overthruster, and the specimen of alien/transdimensional life he obtained while traversing the 8th dimension, Banzai is called to the phone, where he receives an electrical shock. Simultaneously, strange men disrupt the event and kidnap Hikita. When Banzai returns, his electrical shock enables him to recognize them as humanoid aliens, and he gives chase. He rescues Hikita, and they evade the aliens long enough for the Cavaliers to rescue them.

Banzai and the Cavaliers return to the Banzai Institute, where they are met by John Parker, a messenger from John Emdall, the leader of the peaceful Black Lectroids of Planet 10. Parker delivers a recording from Emdall in which she explains that her people have been at war with the hostile Red Lectroids for years, managing to banish them to the 8th dimension. Lizardo's failed test of the overthruster in 1938 allowed the Red Lectroids' tyrannical leader, Lord John Whorfin, to take over Lizardo's mind and enable several dozen of his allies to escape. Because Banzai has now perfected the overthruster, Emdall fears Whorfin and his allies will try to acquire it to free the other Red Lectroids and tasks Banzai with stopping Whorfin; otherwise, the Black Lectroids will attack Russia from their orbiting ship, triggering a nuclear World War III that will annihilate the Red Lectroids on Earth as well as humankind.

The Cavaliers track the Red Lectroids to Yoyodyne Propulsion Systems in New Jersey. They realize that Orson Welles's broadcast of The War of the Worlds described the Lectroids' arrival in Grovers Mill, New Jersey in 1938, though afterward the Lectroids forced him to state it was fictional. Yoyodyne has been building a spacecraft to cross over to the 8th dimension, disguised as a new United States Air Force bomber. While the Cavaliers plan their response, Red Lectroids break into the Institute and kidnap Penny, unaware that they have also captured the overthruster, which she was carrying.

At Yoyodyne, Penny refuses to tell the Red Lectroids where the overthruster is, and they begin torturing her. Banzai enters Yoyodyne headquarters alone; the Cavaliers soon follow, reinforced by several groups of the Blue Blaze Irregulars—civilians recruited to assist the Cavaliers. Banzai saves Penny and fights off the Red Lectroids, though she is wounded and unconscious. While the Cavaliers tend to her, Banzai and Parker sneak into a pod on the Yoyodyne spacecraft. Lacking Banzai's overthruster, Whorfin insists they use his imperfect model, which fails to make the dimensional transition; instead, the Red Lectroid spaceship breaks through the Yoyodyne wall and takes off into the atmosphere.

Lord Whorfin ejects the pod containing Banzai and Parker from the craft, but they activate it and use its weapon systems to destroy Whorfin and the other Red Lectroids. Banzai parachutes back to Earth while Parker returns to his people in orbit using the pod. With the situation resolved and war averted, Banzai finds Penny, who appears to have died from her injuries. When he gives her a farewell kiss, Emdall allows Banzai one more brief moment of electricity, reviving Penny.