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Victoria Siebert is the secondary main antagonist in the 2013 film Side Effects by Steven Soderbergh.
She is portrayed by Catherine Zeta-Jones, the Academy Award winning actress who's best known for her role as Velma Kelly from the 2002 musical Chicago.
Emily Taylor goes to Victoria for counseling after her husband Martin's arrest for illegal insider trading bankrupts her and leaves her depressed. Victoria discloses to Emily that her own husband cheated on her and then abandoned her. Over time, they begin a romantic relationship with each other. Then, with Victoria teaching Emily how to fake psychiatric disorders, and Emily in turn teaching Victoria about the world of stocks and economics, they begin a plan to kill Martin and defraud the stock market to make money.
Once Martin is freed from prison, Emily begins attempting suicide (both attempts are faked). Emily's doctor, Jonathan Banks (played by Jude Law) is then advised by Victoria to prescribe a new anti-depressant, Ablixa. Soon after she is prescribed (despite not taking any of the pills), Emily's depression begins to end, but she experiences the drugs side effects, one of them being bouts of sleepwalking. Victoria was the only certified psychiatrist who claimed that Ablixa causes sleepwalking, proving that the side effect was fabricated to bolster Emily and Victoria's plan.
After Emily murders Martin (during a faked sleepwalking episode), Emily is tried but is advised by Jonathan to plead insanity to avoid her getting sent to prison. Emily is found not guilty under the condition that she be checked into a mental ward until she is cleared by a psychiatrist. With Ablixa's side effects being tied to Martin's murder, Ablixa's stock prices plummet while the stocks of a rival company soar. Emily and Victoria had anticipated this, buying stocks in the competitor before the murder and becoming rich off the stocks' increase in value.
After the case's bad press leaves his career in shambles, Jonathan starts getting suspicious of Emily's behavior, and after several tests and research prove that Emily was lying the whole time, Jonathan confronts Victoria about it. In order to set him back, Victoria sends compromising pictures of Jonathan and Emily together, as well as some sultry solo pictures of Emily in bed to his wife, causing her to leave him. Unbeknownst to Victoria, Jonathan had once been accused of having an affair with one of his clients, which is why his wife was so quick to believe the photos to be valid.
Jonathan, undeterred, uses legal means and loopholes to prevent Victoria and Emily from seeing each other, leading the latter to believe that Victoria is selling her out to him. To prevent this, Emily confesses their entire plot to Jonathan and offers him a deal. In return for declaring Emily sane so she can leave the mental ward, Emily will offer Jonathan a large sum of money to restart his practice and also turn in Victoria.
Emily returns to see Victoria and the two are about to make love, with Victoria talking about her role in Martin's murder. She soon finds out that Emily was wearing a wire, and with her confession heard by the police (who were waiting outside), Victoria is arrested for conspiracy to commit murder.