Ostensibly the film is "suggested by" the so-named story by Edgar Allan Poe, and Lugosi's character is saddled with an irrational and irrelevant feline phobia. The connection is contrived, a movie executive's attempt to stack the deck even further with some name recognition coming off of Murders in the Rue Morgue. This Black Cat has nothing to do with Poe or cats and would have done just as nicely without them.
Universal's first Black Cat opens with Peter and Joan Allison on their European honeymoon. Just as they settle into their private cabin on the Orient Express, a scheduling mix-up forces them to share with Dr. Vitus Werdegast, played by Lugosi. The amiable psychiatrist is on his way, so he says, to visit his old friend Hjalmar Poelzig in Hungary. At night he also gets a little too familiar, surreptitiously stroking Joan's hair. Peter, played by Dracula alumni David Manners, sees this but Werdegast tries to put him at ease with an explanation. Joan looks very much like the wife he lost 18 years before when he was called away to serve the Austro-Hungarian Empire in The Great War. At the very end of the war he was captured in the Massacre of Fort Marmorus, during which thousands of Hungarians, soldiers and civilians alike, were brutally murdered. The valleys were piled flush with bodies and the rivers ran thick and red. They were the lucky ones. Werdegast explains how he was sent to the prison camp where he remained for 15 years, his soul destroyed though his body survived. Now free, he is returning to his homeland to find his wife and child.
Arriving at their stop, the trio embark by cab, the honeymooners to their next destination and Werdegast to the home of Poelzig, an avant-garde architect. An accident kills the cab driver and injures Joan, so the whole troupe must shelter at Poelzig's mansion. Unusual for Universal, it is not a decrepit old manor house full of cobwebs and Gothic arches. On the contrary, it is a sleek, new, ultra-modern abode in the Bauhaus style. After all the commotion, Werdegast and Poelzig, who is Karloff of course, meet and the truth is revealed: it was Poelzig, as commanding officer, who betrayed the fort to the Russians and became the architect of genocide. His brightly-lit, polished chrome house of the future is built upon the very ruins of the fallen outpost, the scene of his crime, overlooking thousands of rudely carved crosses. The reason for his atrocity was a shared, jealous love for Werdegast's wife... An infatuation that caused him to preserve her corpse under glass when she died more than a decade before, possibly by his own hand. To top things off, Poelzig lies about Werdegast's daughter, for she is not dead. She is now Poelzig's wife.
Between the two men is a mutual hatred so deep that it would not be satiated with merely killing one another. Poelzig wants to obliterate what's left of Werdegast's fractured soul and Werdegast would like nothing more than to strap Poelzig in and flay him alive. Revenge becomes an intricate game of living chess with the American honeymooners caught in the middle. Every maneuver comes to a head on the following night, in the dark of the moon when Poelzig gathers his followers for a dark, Satanic mass with Joan as the intended ritual sacrifice.
All of this in one Universal Monster film of the Thirties. Karloff as the utterly unsympathetic villain, Lugosi as the murderous hero, evil Satanic rites, Bauhaus architecture, the first direct reference to the horrors of World War I that did much to inspire the whole series, and overtones of necrophilia and incest... The Black Cat is definitely a pre-Code feature that no doubt did its part, despite its success, to provoke a negative reaction out of audiences. Eventually Universal would push too hard and the series would go on hiatus after the next Karloff-Lugosi outing. Thereafter, The Black Cat was remade in 1941, also with Lugosi playing a bit-part opposite Basil Rathbone in a somewhat disappointing Old Dark House murder mystery.
Quite possibly one of the time's most inappropriate advertising gimmicks.