Dr. Paul Carruthers is a chemist who designed a perfume for a cosmetics company. Said perfume then wound up making his partners a fortune, while Carruthers—who'd sold off his partnership stake in the company—was left with nothing but a relatively paltry $5,000 bonus. Out of a misplaced sense of revenge, Carruthers decides to experiment on a bat to make it large and ravenous. He then trains it to kill anybody wearing an aftershave he designed and gave to his perceived enemies as a "gift".
Followed by two sequels, Devil Bat's Daughter (1946) and Revenge of the Devil Bat (2015).
This film contains examples of:
- Antagonist Title: Referring to the nickname the press gives the giant bats.
- Bat Out of Hell: Dr. Carruthers has a giant bat he uses to kill his enemies.
- Big Bad: Dr. Paul Carruthers, master of the Devil Bat.
- Honest Corporate Executive: Despite Carruthers' claims, Heath and Morton are perfect to honest, having given him the option of joining the company or selling off the stocks. Even after Carruthers chose the latter, they gave him a check for $5,000—equivalent to $87,000 today—as a show of gratitude.
- Lightning Can Do Anything: Electrical impulses can make bats grow exponentially.
- Omnidisciplinary Scientist: Carruthers does work in medicine (town doctor), chemistry (designing perfumes), biology (experimenting on the size of bats) and psychology (conditioning bats to react violently at certain scents).
- The Sociopath: Dr. Paul Carruthers, who makes giant bat monsters to kill the corporate executives he sold his makeup formulas to, and their entire families, because he didn't believe he got enough credit despite the fact that they were completely upfront with the fact that they'd be using it for profit.
- Villain Opening Scene: Carruthers finishing his bat growth experiments.
- Villain with Good Publicity: Dr. Carruthers is a vengeful murderer with a reputation as a kindly small town doctor.