- "I have never done anything for anybody who couldn't do something for me. I string along an eager kid with promises I'll pay him money. I only keep him around because he looks up to me. Adam, if you're watching, don't be a publicist. You're too good for it. I lie in person and on the phone. I lie to my friends. I lie to newspapers and magazines who, who sell my lies to more and more people. I am just a part of a big cycle of lies, I should be fuckin' president. I wear all this Italian shit because underneath I still feel like the Bronx. I think I need these clothes and this watch. My Two thousand dollar watch is a fake and so am I. I've neglected the things I should have valued most. I valued this shit. I take off my wedding ring to call Pam. Kelly, that's Pam. Don't blame her. I never told her I was married. And if I did she, she would have told me to go home. Kelly, looking at you now, I'm ashamed of myself. Allright? I mean, work so hard on this image, on Stu Shepherd, the asshole who refers to himself in the third person that I only proved I should be alone. I have just been dressing up as something I'm not for so long, I'm so afraid no one will like what's underneath. But here I am, just flesh and blood and weakness, and uh and I love you so fucking much. And, um, I take off this ring because it only reminds me of how I've failed you, and I don't, don't want to give you up. I want to make things better, but it may not be my choice anymore. You deserve better."
- ―Stu's speech.
He was portrayed by Colin Farrell.
Stu Shepard is an arrogant New York City publicist who has been courting a woman named Pam behind his wife Kelly's back. He uses the last remaining public phone booth in the city to contact Pam so his wife can't notice them on the phone bill. During the call, he is interrupted by a pizza delivery man, who attempts to deliver a free pizza to him, but Stu rudely turns him away. As soon as Stu completes his call to Pam, the phone rings. Stu answers, to find that the caller, who knows his name, warns him not to leave the booth, and says he will say hello to Pam for him. He also says he will call Kelly, leaving Stu panicked.
The caller tells Stu that he has tested two previous individuals who have done wrong deeds in a similar manner, giving each a chance to reveal the truth to those they wronged, but in both cases, neither agreed and were killed. To demonstrate the threat, the caller fires a suppressed sniper rifle at a toy robot sold by a nearby vendor; the damage is unseen by anyone but Stu and the caller himself. The caller demands that Stu confess his feelings for Pam to both Kelly and Pam to avoid being killed. The caller contacts Pam, and puts her on line with Stu, who reveals that he is married. The caller then hangs up, telling Stu to call Kelly himself.
As Stu hesitates, the booth is approached by three prostitutes demanding to use the phone. Stu refuses to leave, having been warned by the caller to stay in the booth and not reveal the situation. Leon, the prostitutes' pimp, joins his charges, smashes the side of the booth, grabs at Stu in a headlock and starts punching him. The caller offers Stu to "make him stop" and asks if he can hear him, which Stu just answers positively causing the caller to misunderstand Stu that he wants him to shoot Leon. The caller does and Leon staggers away before collapsing dead in the street. The prostitutes immediately blame Stu, making a scene over Leon's body, accusing him of having a gun as the police and news crews converge on the location. Police Captain Ed Ramey, already suspecting Stu of being the killer, corners the streets with police roadblocks and starts trying to negotiate with him to leave the booth, but Stu rejects, telling the caller that there is no way they can incriminate him; the caller proves him wrong, pointing to a handgun that was planted in the roof of the phone booth. Both Kelly and Pam soon arrive on the scene. The caller demands Stu tell Kelly the truth, which he does. The caller then orders Stu to choose between Kelly and Pam, and the woman he does not choose will be killed.
While on the phone with the caller, Stu secretly uses his cell phone to call Kelly, allowing her to overhear his conversation with the caller. She, in turn, quietly informs Captain Ramey of this. Meanwhile, Stu continues to confess to everyone that his whole life is a lie, to make himself look more important than he really is. Stu's confession provides sufficient distraction to allow the police to trace the payphone call to a nearby building, and Ramey uses coded messages to inform Stu of this. Stu warns the caller that the police are on the way, and the caller replies that if he is caught, then he will kill Kelly. Panicked, Stu grabs the handgun and leaves the booth, screaming for the sniper to kill him instead of Kelly or Pam. The police fire upon Stu, while a smaller force breaks into the room that the caller was tracked to, only to find the gun and a man's corpse.
Stu regains consciousness to find the police only fired rubber bullets at him, stunning but not harming him. Stu and Kelly happily reunite. As the police bring down the body, Stu identifies it as the pizza delivery man from earlier. Stu gets medical treatment at a local ambulance; as he does, a man with a briefcase passes by and says that he regrets killing the pizza deliverer and warns Stu that if his new-found honesty does not last, he will be hearing from him again. The man disappears into the crowd with Stu unable to call out because the ambulance paramedic had just given him morphine. Stu passes out as the caller walks away unnnoticed.