Since 1938, Halloween and alien invasions go hand-in-hand...
...even when the "aliens" are from inside the Earth, rather than outer space!
This story from Avon's Strange Worlds #3 (1951) was a "Fleagle Gang" production.
The "Fleagles" were a group of artists including Frank Frazetta, Al Williamson, Roy Krenkel, Wally Wood, Angelo Torres, and George Woodbridge who would help each other out on tight deadlines by doing a "jam" with individuals penciling and inking different pages and even different panels on a single page, producing some absolutely amazing visuals!
Trivia: the group was named by EC Comics editor/writer/artist Harvey Kurtzman.
The idea of advanced beings living inside the Earth and invading/reconquering the surface was very popular in the early 1950s.
Richard Shaver and pulp magazine editor Ray A Palmer caused a media firestorm with series of stories presenting a theory that combined the "civilization inside the Earth" concept with another pop culture phenomenon...flying saucers!
Numerous readers wrote in, claiming that they had actually seen creatures and vehicles exactly as described in the stories!
The "Shaver Hoax" (as it came to be known) influenced 1950s sci-fi/fantasy ranging from the pilot episode of the TV's Adventures of Superman to movies like Brain Eaters.