The Purple Monster Strikes

Layton observes what he believes to be a meteorite landing far away and decides to investigate. He contacts his niece Sheila and asks her to bring Craig Foster to help analyze the discovery, then heads out to search for a crater. The moment sets the tone for a night that will reveal something far stranger than a simple meteor.

Instead of a meteor crater, Layton finds a crashed spacecraft. The ship's pilot emerges and claims to be from Mars, introducing the premise that the visitor is not from this world. Layton's curiosity quickly gives way to a dangerous encounter.

Believing the alien to be friendly, Layton brings him back to the observatory. The Martian, calling himself The Purple Monster, wants to study Layton's airplane designs and soon reveals his plan to steal them. He intends to build a fleet to invade Earth using a new spaceship.

When Layton objects, the Martian uses a weapon that emits carbo-oxide gas and kills him instantly. The alien then transforms into a ghostlike form and takes over Layton's body, beginning to masquerade as the scientist. Sheila and Craig—who work with Layton's foundation—are duped as the ruse continues.

Inhabiting Layton's body, the Martian witnesses the unrelated theft of the plans by Garrett. He convinces Garrett and his gang to aid in the invasion plot. The alien's disguise as Layton helps coordinate the early stages of the invasion by guiding the spaceship project.

The Purple Monster uses the criminals to further his takeover, convincing them to help steal more materials and build the spaceship. Construction of the craft begins under the illusion of legitimate work overseen by Layton. The Earth remains oblivious to the deception as the countdown to invasion starts.

Craig Foster and Sheila start noticing discrepancies in Layton's behavior and the missing documents. They begin actively working to thwart the Martian's plan, dealing with mind-control poisons, carjackings, and threats from the alien's henchmen. The pair becomes the primary resistance against the invasion plot.

Sheila is lured to the gang's hideout where danger awaits. Foster extracts information from a captured gang member and races to save Sheila before the explosives detonate. The tension escalates as the trap nears its deadly moment.

Inside the hideout, an electric eye triggers a deadly booby-trap with explosives. Sheila is able to remove her gag and warn Foster, allowing a narrow escape. Foster shoots a henchman, causing him to fall into the eye and detonating the bomb.

Foster and Sheila devise a plan to reveal the Martian's deception. Sheila is to visit downtown to sign papers while Foster installs a movie camera in Layton's office that will trigger remotely when the phone rings. Foster then summons reinforcements to search the observatory, which has become the alien's hideout.

Craig and Sheila reach the observatory only to find it deserted. Sheila descends to the basement and discovers the Purple Monster's subterranean lair, where she is seized. Foster searches frantically for her, and the lair hints at the true extent of the alien's control.

Craig Foster discovers the alien's hideout, and a plan unfolds to stop the invasion. He uses part of the spaceship—a sonic pulse cannon—to shatter the Martian's craft. The Purple Monster is trapped inside the ship as it explodes, ending the threat to Earth.