Our Super-Spoilery Interview With the Cast of 'The Girl on the Train' About That Twist Ending

Warning: This post and the above video contain massive spoilers for the ending of The Girl on the Train, so proceed at your own risk.

Admit it: You thought the culprit behind the mystery at the center of The Girl on the Train was the girl on the train, right? You’re in good company, because the film’s star, Emily Blunt, had the same assumption before she got to the end of author Paula Hawkins’s twist-filled novel on which the new movie was based. “In a way, I thought that it was Rachel,” the British actress says about the emotionally troubled character she portrays in the Tate Taylor-directed adaptation. “I was really surprised and betrayed and sort of gut-wrenched by the fact she’d been manipulated.”

If you’ve seen the movie, which topped the box-office charts in its opening weekend, you know that Rachel’s manipulator is none other than her ex-husband Tom, played by Justin Theroux. Described by the actor as “either a complete sociopath or a narcissist,” Tom has used Rachel’s alcoholism as a means to gaslight her, leading her to believe she was responsible for the end of their marriage and his affair with current wife Anna (Rebecca Ferguson). What neither Anna nor Rachel knew is that Tom was also sleeping with Megan (Haley Bennett), whose sudden disappearance sets the story in motion and makes Rachel a person of interest to the police.

By the end of the film, Rachel pieces together that her ex hasn’t been truthful — or, for that matter, faithful — to her for years, and confronts Tom in his home while Anna looks on. He responds by beating her and revealing that he killed Megan after she told him she was pregnant. “I think he saw himself as the victim of three horrible women, as opposed to those three women being the victim of one horrible man,” Theroux explains. And Blunt, for one, feels that her co-star fully inhabits his character’s psychology. “He plays it so brilliantly, with such danger and ambiguity. I think it’s his calm that’s the most unsettling thing.”

Watch a video about the location switch in ‘The Girl on the Train’: