Boris tried to tell them House of Frankenstein wasn't his fault, but no one would listen.

On Friday the 13th mild-mannered English professor George Kingsley (Stanley Ridges) is rundown by gangster Red Cannon, himself shot during a gun battle with former associates.  Kingsley’s brain is severely damaged, so his friend and fellow professor, Dr. Ernst Sovak (Boris Karloff, The Invisible Ray),  transplants part of the wounded gangster’s brain to save Kingsley’s life (and prove his theories in the bargain).  Sovak’s motives aren’t entirely pure, however, as Red hid most of his ill-gotten-gains and Sovak hopes that he will be able to get the information out of Kingsley when he recovers.  To aid in the process, Sovak takes Kingsley to New York, deliberately bringing him to Red’s old hang-outs in the hopes of awakening Red’s consciousness.

"I vant to rub your back"

Sovak’s theories prove correct and soon Kingsley and Red are doing the Jekyll and Hyde thing, with the main trigger being the sound of sirens.  Red uses his new body to gain terrible revenge on his former associates, strangling them one by one, and to see his girl, nightclub singer Sunny Rogers (Anne Nagel, Mighty Joe Young).  Rogers, disturbed by Kingsley’s intimate knowledge of Red’s affairs, agrees to bait a trap for Red/Kingsley with Eric Marnay (Bela Lugosi, Bride of the Monster), Cannon’s former partner.  Marnay does not believe Red is back, but that Red gave Kingsley the location of his loot in return for enacting Red’s revenge.  Will Red remain dominant long enough to find the money and defeat Marnay and his thugs?  Will Sovak be able to return Kingsley to control and keep him out of jail?

It's his life, and it's his wife

Black Friday is generally considered one of the lesser Universal horror films, in no small part because it barely qualifies as horror.  Writer Curt Siodmak grafted a cheesy brain transplant plot onto a “gangster back from the dead wants revenge” plot, and threw in some Jekyll/Hyde for good measure.  Karloff and Lugosi fans may find that amount of time given to Stanley Ridges’s (quite effective) dual role disappointing as Black Friday under-utilizes Karloff’s mad scientist (who mostly supplies the impetus for the plot) and Lugosi’s gangster.  Lugosi was originally cast as Dr. Sovak and Karloff as Kingsley/Cannon, but Karloff’s gangster act was deemed unacceptable, quite strange considering Karloff’s early and effective role as a gangster in the original Scarface.  Lugosi’s atypical gangster part is more enjoyable than another mad scientist role, as it really is something to see him  ham it up as a gangster.  One suspects it would be easier to buy Lugosi as the duplicitous Sovak than Karloff, whose constant quest for money feels like an added on plot point, one of the rare times Karloff weighs a picture down.

"Before there was Friday the 13th there was...Black Friday"

Black Friday‘s odd combination of gangster revenge picture and mad scientist is reminiscent of 1940s radio thrillers, where such combination of crime and weird science were common.  Ridges plays his dual role well, and, if the science doesn’t make any sense, the film delivers plenty of action, murders, and exciting moments (fight choreography fans will particularly enjoy a fist fight in which Ridges seems to be an early proponent of Kirk Fu), all at a brisk pace.

Check out the trailer, which features some absolutely brilliant (and false) ballyhoo about Lugosi being hypnotized to add realism to his depiction of suffocating: