A group of medical students observe Dr. Jekyll Mark Blankfield performing brain surgery at Our Lady of Pain and Suffering Hospital in Los Angeles, California. Hubert Howes [Peter Brocco], the world’s richest man, watches a recording of the procedure from his hospital bed, hoping to recruit Jekyll to perform the world’s first total transplant, replacing every organ at once. Howes threatens to blow up the hospital if his plan doesn’t go through. Dr. Carew [Michael McGuire], the hospital overseer and Jekyll’s future father‑in‑law, forbids Jekyll from marrying his daughter, Mary, if he refuses Howes’ demands.
Jekyll works in the charity ward, where Mary [Bess Armstrong] visits, complaining that she missed their lunch date because he was busy with patients. Dr. Knute Lanyon [Tim Thomerson] flirts with Mary, adding a note of personal tension to the professional stakes. After Mary leaves, Ivy Venus [Krista Errickson] flirts with Jekyll and invites him to visit her at the nightclub where she works.
Back in his lab, Jekyll measures two white powders on a square mirror. Exhausted and unfocused, he drops the powders, falls asleep, and accidentally inhales the drug, triggering a dramatic transformation. With an air of wild confidence, he indulges further, steals a car, and heads to Ivy’s club. After Ivy performs onstage, she takes him to her room backstage, where he introduces himself as Hyde and they become intimate. The next morning, Jekyll, filled with regret, declares his unwavering love for Mary.
Over the next days, Jekyll tries to dispose of the drug but keeps returning to inhalation, leading to a string of comic and sexually charged escapades that complicate his life and loyalties. Jekyll wins a research grant and is invited to a ceremony in London. Hoping to use the prize money to win Ivy’s affection, Hyde tracks her to an arcade and invites her to accompany him abroad. Ivy says she prefers Jekyll to Hyde. When he reveals that they are the same man, she doesn’t believe him; in a moment of frustration, he destroys an arcade game, and Ivy is electrocuted.
Hyde makes his way to Los Angeles International Airport and climbs onto the back of a plane bound for London. Ivy survives and travels to London by train, vowing revenge. At the ceremony, George Chakiris accepts the award on the doctor’s behalf, declaring that the remaining vial of Jekyll’s substance will be donated. Hyde swings down from the balcony, grabs the microphone, and sings, drawing the attention of the audience to his dual identity. Realizing that Hyde is the same man she loves, Mary becomes aroused by his new persona, while Ivy watches from the crowd. Hyde bolts from the hall, chased through foggy streets by the audience, and eventually falls from a building. When he wakes, he again claims that the drugs have unveiled the two halves of his split personality. Mary longs for Hyde, while Ivy wants Jekyll, and the two women drag him through a cemetery to negotiate a strange arrangement.
Nearby, the skeletal corpse of Robert Louis Stevenson rolls over in its grave.
