Like many American International films of its era, How to Make a Monster was sold to distributors on the basis of its title alone: only after theatrical play dates had been established did anyone get around to writing a script! Robert H. Harris plays Pete Drummond, who according to the script has been chief makeup man at American-International for 25 years, or approximately 20 years before the studio was actually established. When the studio is sold, Pete is brusquely informed that neither he nor his monster creations -- notably the Teenage Werewolf and Teenage Frankenstein -- will be required any longer, inasmuch as American International is going to concentrate on musicals from now on. Angered and humiliated, Pete takes revenge on the callous studio heads by hypnotizing a couple of actors (Gary Clarke and Gary Conway) into believing that they're genuine monsters. Under Pete's control, the two thespians begin committing murders left and right, wreaking havoc throughout the American International lot.