He contacts his niece Sheila and asks her to bring Craig Foster to the observatory to help analyze his discovery; he then sets out to search for the meteorite crater.

Doing so fools the astronomer's niece Sheila and criminologist Craig Foster, both of whom work with Dr. Layton's foundation, which is responsible for commissioning the spaceship project.

Inhabiting Dr. Layton allows the Martian to witness the unrelated theft of the plans by a gangster named Garrett.

The closest the criminals come to succeeding is in Chapter 7 ("The Evil Eye"), when Sheila is lured into a trap at the gang's hideout.

Foster gets the information out of a captured gang member and speeds to the house to save Sheila, who has been tied up and gagged inside a room filled with explosives set to detonate after an electric eye is tripped.

However, at the beginning of Chapter 8, Shelia manages to remove her gag and alert Foster about the eye, allowing him to jump over it.

In the last chapter Craig and Sheila realize that the Purple Monster is using Professor Layton's body; they devise a plan to uncover the truth.

Foster then escapes and calls the office to advise him that he will be bringing reinforcements to search the observatory, which he has discovered is the Purple Monster's hideout.

The story ends with Craig Foster using a part of the spaceship, a sonic pulse cannon used to shatter meteors.

He destroys the alien spaceship with the Purple Monster inside as he attempts to fly back to Mars to lead an invasion fleet against Earth.

[6] Roy Barcroft lived close (about a mile) to Republic Studios and jogged to work to keep fit for this job.

[5] The Purple Monster costume was re-used in Flying Disc Man from Mars (for Mota), Radar Men from the Moon (for Retik) and Commando Cody (the agent played by Stanley Waxman).