Emily Taylor is the hidden main antagonist in the 2013 film Side Effects directed by Steven Soderbergh.
She is portrayed by Rooney Mara, who is best known for her roles as Erica from The Social Network and Lisbeth Salander from the American remake of The Girl with the Dragon Tattoo, for which she was nominated for the Academy Award for Best Actress.
Emily and her husband, Martin, lived a lavish life together. However, Martin was arrested and imprisoned for insider trading. The imprisonment ruined them and forced her into a less-than-favorable lifestyle.
Emily began feeling depression and hatred because of her husband's unsafe business practices and goes to Dr. Victoria Siebert (played by Catherine Zeta-Jones) for counseling. After revealing to her that her own husband cheated on her and abandoned her, Victoria and Emily become lovers and conspired to kill Martin and make money at the same time.
With Victoria's knowledge of how to fake psychiatric disorders along with Emily's knowledge of the stock market, they began their plan.
After Martin is released from prison (the beginning of the film), Emily, shortly after, creates a fake suicide attempt by crashing her car in her company's parking lot wall. She is then prescribed anti-depressants from Dr. Jonathan Banks (played by Jude Law) (who is completely unaware of the scheme). Victoria comes to Jonathan and recommends Ablixa to him, a new up-and-coming anti-depressant.
When Emily claimed that her prescription didn't work (she didn't take any of them) and faked another suicide attempt by almost stepping in front of a subway, Emily is promptly prescribed Ablixa. She does take the pills (although later admits that "they didn't do anything for her") and she begins faking the pills' side effects, one of them being bouts of sleepwalking (a side effect "observed" by Victoria).
One night, when Martin comes home, Emily is making dinner while in a faked trance, cutting vegetables with a large chef's knife. Emily then stabs Martin to death before she fakes the scene of her discovery of Martin's murder (tears on her pillows, etc.). Emily is soon arrested for Martin's murder.
In the resulting court case, Emily pleads insanity under the advice of Jonathan, hoping that he can get her out of prison. Emily is found not guilty on Martin's murder under the condition that she stay in a mental institution until cleared by a psychiatrist. With Ablixa 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.
Jonathan, his career in shambles after the case's bad publicity, soon discovers that Emily faked her suicide attempts and was conspiring with Victoria to murder Martin. Then, he goes to meet Emily to conduct an interview, giving her a truth serum. She acts groggily to the serum and answers Jonathan's questions, unaware that the serum was actually a saline placebo, thus confirming his suspicions.
When Jonathan tries to prevent Victoria from seeing Emily through legal means and making Emily believe that Victoria is selling her out for a better deal, she explains her plot to Jonathan and strikes a bargain with him. In return for a large sum of money that will allow Jonathan to restart his medical career and selling out Victoria, he will release Emily from the psychiatric ward under his care and supervision.
Later, Emily sees Victoria again and as they begin to make love, Victoria admits the details and her role in Martin's murder, which is picked up by a wire worn by Emily, and the police arrive to arrest Victoria. Because of double-jeopardy, Emily is no longer criminally responsible for Martin's murder, and thus, she can go free.
Still upset for Emily's plan nearly ruining his professional and personal life, Jonathan gets back at her by prescribing her an unnecessarily large amount of drugs with serious side effects as her caretaker. Along with regular urine tests to prevent her from not taking the drugs, he threatens to send her back to the ward if she doesn't take the pills. Furious with this, Emily rants about all that she had done to murder Martin and avoid prison. A policeman, Emily's lawyer, and Martin's mother overhear the entire rant outside Jonathan's door, and Emily's confession gets her taken into custody by the police and sent back to the mental ward.
- Though Emily and Victoria serve as the Big Bad Duumvirate of the film, Emily is the Bigger Bad of the two because she had bigger plans than Victoria.