Dr. Richard Jacks, Tim Daly, is a talented but frustrated perfumer at a major fragrance company. Despite his skill, his projects keep failing, and the chief executive, Mrs. Unterveldt, rejects his latest creation, insisting it sounds like a woman’s scent and that a woman should work on it. After his great-uncle dies, Richard attends the will reading and learns he is the great-grandson of Dr. Henry Jekyll. This revelation sparks a risky idea: he decides to add more estrogen to the original formula, hoping to perfect it.
He ingests the serum, but at first nothing happens. Then, as he rushes to a job interview at a restaurant, a spilled coffee and his mounting excitement about a potentially higher salary trigger the transformation. His nails lengthen, arm hair recedes, his voice shifts, and his male anatomy reshapes into a vagina inside his pants. His hair grows, and when a waiter dabs at his chest, the swelling becomes visible. Desperate, he races to a mirror and, in a final moment, catches a glimpse of a flawless pair of breasts before tearing off his shirt in shock.
Pete, Jeremy Piven, discovers the transformed woman in the laboratory shower. She caresses herself seductively, then steps out, and Richard—the man behind the metamorphosis—can only utter a stunned, “Wow.” Adopting the alias of "Helen Hyde", the new persona beguiles his colleagues and quickly positions herself as his new assistant. Helen adds to his scent report, flirts with his superiors, Yves DuBois and Oliver Mintz, and treats herself to a shopping spree paid with Richard’s credit cards. The seductive ruse deepens when Helen befriends Richard’s fiancée, Sarah Carver, and convinces her to move out of Richard’s apartment.
The next day, Richard returns to the office to find Helen’s influence already making waves. He realizes he doesn’t remember turning into Helen, and when he visits Sarah, he learns she has moved to his cousin Larry’s apartment. Sarah, though angry, compliments Helen and praises her as fantastic and alive. Richard manages to coax Sarah to a romantic dinner at his place, but the moment he realizes he is turning into Helen again, she flees in confusion. Helen reappears in a leather dress at the office and asks Mintz about a promotion. He dismisses her as merely a secretary, and there isn’t a vacancy to fill.
Pete spots Helen leaving Mintz’s office and, eager to exploit the situation, tries to lure her with a chance to help with his new scent. She initially dismisses him as pathetic but quickly shifts tone, agreeing to go out for a drink. While he’s away washing up, she secretly sabotages his sample, and, with a calm cigarette in hand, watches his desperate screams echo from the lab.
Helen then seduces Oliver Mintz, and they go to his apartment. Oliver agrees to all her demands, thinking he is getting ahead. Everything seems to be proceeding perfectly until a crucial moment: her breast deflates while she’s about to open her teddy. She locks herself in the bathroom, and Oliver misreads the muffled sounds as a powerful orgasm. He attempts a key, then finally busts open the door just as Richard escapes. The next morning, a sharply dressed Oliver informs Richard that he will now be working under Ms. Hyde. When Richard tries to halt the transformation by handcuffing himself in underwear to shoot the process, Sarah interrupts, convinced Richard has become a cross-dressing pervert after finding him in lingerie.
Back at the office, Helen—now impeccably professional—prepares a presentation with Mintz and Dubois to embarrass Richard. Rather than cancel, she steals one of his perfumes and renames it Indulge. At the meeting, both Mintz and Dubois reveal deep infatuation with Helen, and she uses her feminine wiles to her advantage. Dubois is drawn in when she trails a sensual touch beneath the table, prompting him to murmur that it’s “better … much better.” Mintz, initially wary, is convinced to advance the fragrance to Marketing and Design, and the room erupts with maneuvering over who should brief the department.
Helen then creates two videotapes revealing her plan to seize Richard’s body entirely. Richard tries to prove he can still control the situation by stripping naked in his office and writing obscene notes on his own body, but he miscalculates the timing and fails to transform, costing him his job. Helen also intercepts a call from Pete, who intends to prove she stole his work, and she removes him from the equation with a ruthless act.
Sarah is finally convinced when Richard shows her security footage of his initial transformation. He devises a new formula to eradicate Helen, but Sarah must administer it when he finally transforms back. To prevent Helen’s escape, Richard ties his own limbs to a bed, and Sarah attempts to inject the remaining formula. She only manages part of the job before Helen escapes to attend Indulge’s launch party.
Sarah follows Helen into the party and realizes the formula is gradually restoring Richard. As Helen rises to celebrate Indulge’s success, Sarah injects the remaining formula. After a final transformation on stage, Richard is restored to his true self and gives a candid speech to his colleagues, admitting that he had become Helen but insisting he needed to live as a woman to truly understand them. His boss rehires him with a promotion and some vacation time to recover. Richard exits the party with Sarah in hand.
A postscript reveals the fates of the various players, closing the strange chapter on a story that began with a fragrance and a dangerous curiosity.
