Notes: Hammer, 96 minutes.
Dr. Henry Jekyll: Ralph Bates
Hyde: Martine Beswick
Professor Robertson: Gerald Sim
Susan Spencer: Susan Brodrick
Howard Spencer: Lewis Fiander

Directed: Roy Ward Baker
Produced: Albert Fennell & Brian Clemens
Written: Brian Clemens

Summary: We see a dead rabbit at a street sales stall. A man stalks a prostitute in Whitechapel. He stabs her, and with a scalpel removes something of hers, placing it on ice in a small box. This turns out to be a flashback from Dr. Jekyll, writing a "testament" and introducing himself as "age 30, male." Jekyll's friend Professor Robinson meets the Spencer siblings, Susan and Howard, who live upstairs from Jekyll (at #13) who, it is decided, works "far too hard" on his anti-virus experiments against diphtheria. When Robinson tells him that he'll be dead before he can possibly make any significant progresses in medical science, Jekyll becomes obsessed with immortality and works "towards the black abyss." He visits the morgue regularly and his experiments are bloody. But he manages to keep a fly alive for several days instead of its lifespan of a few hours, so he's onto an elixir of life, involving female hormones. But the originally male fly has laid eggs.

Burke and Hare (who lived decades earlier than the 1880s and not in London) supply Jekyll with corpses of girls no older than 20. They kill a tavern girl. Jekyll turns down a dinner invitation from the interested Susan, and her brother wonders, "Too busy? Or impervious to women?" Jekyll downs a concoction, gasps a lot, and sees a woman staring back at him from the mirror. Howard catches a glimpse of who he thinks is Jekyll's girlfriend. Female Jekyll laughs until she sees that her own hand on her breast is male. S/he passes out and wakes as Jekyll. Susan is snippy until he tells her the woman is his sister, the widowed Mrs. Hyde.

Burke is lynched by a disgusted mob and Hare is thrown into a lime pit, ending up a blind beggar. Susan tells Jekyll, "I think you're noble," when they discuss the weighing of evil against eventual good. Jekyll reasons that he must take life to prolong it. So he murders a gentleman-obsessed whore. Robinson is consulted by the police and says the slashing was "expertly done." Jekyll takes another drink just as Susan is delivering a supper tray. He rushes her out, transforms, and, as Hyde, toys with Howard. Hyde says of Jekyll, "He hasn't been himself of late." Jekyll stabs another woman and makes an extraction in the streets, but this is getting dangerous. It's the "same devilish hand," declares Robinson. Susan visits Jekyll, who claims to be burning chemical-stained clothing. A mail-order arrives (a dress) and Jekyll piches a fit because something is wrong.

Robinson and a cop stake out Jekyll's place at night. Jekyll realizes it and reasons that they're expecting to see him, a man, leave. He transforms, and Hyde puts a knife in her stocking. She goes to Whitechapel and stalks a drunken whore who says with relief, "Oh, it's only a lady." She gets stabbed. So the cop is called away from the stake-out just as Hyde returns home. "It's a queer business, sergeant, very queer."

Jekyll seems gay to Howard. Jekyll shouts "no" to the mirror. But he soon finds he has lost resistence and Hyde murders with some freedom. Robinson visits and finds Hyde, confessing "grave suspicions" about Jekyll to her. They need, says Hyde, to talk elsewhere, and Robinson seems titillated by the notion that she would be "unchaperoned." She succeeds in murdering him, and although it seems as if it may have been a dream from which Jekyll awakens, he is bloody. He throws the knife into the mirror and rampages in his lab. Hyde is dominant and want to be rid of Jekyll. Hyde invites Howard in for a make-out session, and Howard remarks, "If you could imagine what a man feels...." But Hyde says she can. Susan interrupts them, and Hyde reassures her that Jekyll is fond of her as Hyde is fond of Howard. Alone, the inner sides of Jekyll contend for dominance. He sees a distored face in the mirror: "We'll see who wins." Jekyll tells Susan to stay away from his sister: "She means great harm." Jekyll is late for a date with Susan as he agonizes over a dress. For Hyde, tonight there will be a different kind of victim: a fresh young virgin." Hyde stalks Susan in the fog, but Jekyll's masculine hand prevents the stabbing.

The blind man, Hare, connects Jekyll with the Whitechapel ripper murderer. The police come for Jekyll, who escapes only to the rooftops and dramatically keeps slipping until, to the horror of Susan and other onlookers, he falls to his death. His face is a hybrid of male and female. Chemicals eat his text.

Commentary: Despite the gender-blending explorations here, the result depends on and unfortunately reinforces traditional gender roles and assumptions. The only significant implicit commentary concerns how much easier it is for the female to get away with murder because of the lower expectations.