Vincent Sherman's The Return of Dr. X (1939) was meant to be nothing more than an affordable sequel to Warners' earlier two-strip Technicolor shocker Dr. X (1932), starring Lionel Atwill and Fay Wray. Most notable for its rare casting of rising star Humphrey Bogart as a literal dead man walking, this odd little B-picture capped a fascinating decade for American horror films, in which grim situations, graveyard humor and psychologically and physiologically damaged characters were routine – an approach that was softened considerably in the next decade, as Universal's monster rallies made fright films less complicated and less interesting.

The Return Dr. X originated with an original story, "The Doctor's Secret," by British writer William J. Makin. Warners purchased the piece for a small sum and set actor turned writer/director Crane Wilbur to the task of adapting it for the big screen. (Wilbur's stage play The Monster had been adapted in 1925 by Roland West as a vehicle for monster maker Lon Chaney.) Initially, Warners had big plans for the project, dreaming up another Technicolor extravaganza with Frankenstein (1931) star Boris Karloff as a groundbreaking/taboo shattering man of science brought back to life by another surgeon, to be played by Dracula (1931) star Bela Lugosi, who realizes he has created a monster. By the time cameras rolled in May of 1939, budgetary concerns had favored a standard black-and-white presentation and nixed the Karloff-Lugosi reteaming in favor of more affordable actors, while Crane Wilbur's adaptation had been rewritten by Lee Katz.

As in Dr. X, the sequel concerns a series of ghastly murders occurring within the heart of modern New York City, with ace reporter Walt Garrett (Brother Rat's Wayne Morris) and physician Mike Rhodes (Dennis Morgan, later of Kitty Foyle) tracking a killer whose victims share a rare blood type. Discovering the lifeless corpse of stage actress Angela Merrova (Lya Lys, then the girlfriend of director Anatole Litvak), the headline hungry Walt phones in the lead… only to be disgraced the next day when Merrova appears in his paper's city room to demand a retraction. Walt and Mike eventually deduce that Merrova was in fact murdered but returned to a semblance of life by hematologist Dr. Flegg (a monocled John Litel, with a demonic beard that recalls Bela Lugosi's White Zombie voodoo master Murder Legendre ), creator of a type of synthetic blood, who confesses that Merrova was not his first experiment. Earlier, Flegg had resurrected Maurice Xavier, a brilliant but wrong-headed surgeon executed in the electric chair for conducting illegal and inhumane experiments on children.

According to biographer Richard Gehman, Warners contract player Humphrey Bogart was none too happy about this assignment but soldiered through the production (in flammable make-up!), giving the part of the eponymous mad scientist his professional all. Sporting a Bride of Frankenstein streak of white hair, a pronounced limp and a withered left hand, Xavier's damaged body habitus recalls that of Duke Mantee, the convict character Bogart had played in The Petrified Forest (1936), whose hands continued to hang in front of him as if still in handcuffs. Xavier is an remarkably disgusting character, and not only because of clammy, pallid skin that makes him look like "a piece of white marble… like something dead." Xavier's crime is revealed to have been starving children to death in an abandoned hunter's shack in the New Jersey Meadowlands, a plot point that rings all too true in this age of endless sexual predators and high profile child kidnappings. It's amazing that the censors allowed this disturbing backstory and that Bogart (no stranger to refusing assignments), risked career suicide to play it. Of course, The Return of Dr. X did Bogart no harm in the long run. Within two years he was playing Sam Spade in John Huston's The Maltese Falcon (1941) and in three starring in Casablanca (1942) alongside Ingrid Bergman and Claude Rains.

Its climax a batty mixture of Gothic horror tropes (a swampland shack surrounded by lifeless trees with gnarled, twisted trunks and a screaming heroine in Rosemary Lane) and gunplay more suited to a Warners gangster picture, The Return of Dr. X carried forward a morbid streak that had been in evidence in American horror films since Dracula broke box office records nearly two decades earlier. Bogart's Xavier (who cuddles a white rabbit, presumably for its warmth!) is a bona fide "wrong'un" in the tradition of Dracula's fly-eating Renfield, Boris Karloff's necrophiliac architect in The Black Cat (1934), Peter Lorre's Mad Love (1935) headcase Dr. Gogol and Sandor, the creepy manservant of Dracula's Daughter (1935) played so memorably by Irving Pichel; his physical infirmities also recall the disfigured characters of Dr. X and Mystery of the Wax Museum (1932), The Raven (1935), Mad Love (1935), Son of Frankenstein (1939) and The Face Behind the Mask (1941), as well as the medical mishaps of Frankenstein and Island of Lost Souls (1932).

Most of these creatures are not monsters by nature so much as nurture (or the lack thereof), creatures created by circumstance, societal others existing along the fringes of civilization, bastard children locked in society's attic. Life-taking, blood-drinking, flesh-eating, corpse-loving, grave-robbing and profaning God by tampering with the forces of life and death -this was the shock syllabus of American horror between world wars. After the attack on Pearl Harbor and America's entry into World War II in 1941, dark themes and funereal motifs were largely left behind as the nation struggled to remain upbeat. Horror films of the 1940s (most of them sequels to 30s hits) were bigger, brighter, cleaner and easier to laugh off on the walk home. It was truly the end of an era… but it had sure been one hell of a decade.