The movie opens at a small park in Chicago on a winter day. Children are playing and when a ball goes flying out into the woods, a small girl named Emma goes after it. We hear her scream. Her mother jumps up from a table, where she'd been visiting with another adult, and rushes into the woods after her daughter. She finds Emma, hugs her, and takes her away. We see only the ball, with blood on it, but nothing else to indicate what happened, or what caused the girl to scream.In a Chicago courtroom, hotshot Assistant District Attorney Mitch Brockden (Dominic Cooper), is providing the closing argument in a case of assault. He tells his partner, Assistant District Attorney, Stuart Wilson (Dylan Taylor) that the jury will find the defendant guilty and will be sentenced to five years, with parole after two. He then excuses himself and goes home to his wife. Rachel Brockden (Erin Karpluk) and new baby girl, Ella.Mitch apologizes to his wife for having to go a "work thing" that night, preferring to stay home with her and the baby. The "work thing" is a drinking party with his buddies from work. As Mitch says goodnight and tells Stuart and another man that he planned to call a cab to take him home, his cell phone rings. It's an operator telling him he has a collect call from an inmate at Concord Penitentiary. Mitch hangs up. As he calls for a taxi on his cell phone, he notices two men standing close to his SUV and looking in the windows. He approaches and calls out to them, asking if he can help them. They turn and walk away. Mitch decides he doesn't want to leave his car there overnight, so he gets in and starts driving home.A police car pulls out from a side street and follows behind Mitch a ways before turning on it's lights and siren. Mitch thinks he's being pulled over, so he turns off on a side street and is relieved to see the police car continue down the road he had been on. Right then, a man dashes in front of Mitch's car and Mitch can't avoid hitting him. He gets out of his vehicle and rushes over to the man, lying injured in the street. Mitch apologizes, and as he bends over the man, seems shocked to see that the man's face is covered with cuts and abrasions. The entire front of his body is also bloody and seems to be cut up. Mitch removes his jacket and covers the man, then prepares to call 911 on his cell phone. Mitch seems to hear something in the alleyway, where the man he hit came from, and he looks that way, but doesn't see anything. He has second thoughts about using his cell phone, so he rushes across the street to a pay phone and calls 911. He doesn't give his name.Mitch hurries back to the man, telling him that he can't stay, but that an ambulance is on the way. The man begs him not to leave him, but Mitch grabs his jacket and stands up to go. He has to jerk his jacket from the grip of the injured man and his business cards fly out of a pocket and land on and around the man. Mitch scrambles to collect them all, then he jumps in his SUV and leaves.Mitch takes his SUV through a car wash before he returns home, parking in his garage. He disposes of his jacket, scarf, gloves and suit coat, placing them in a garbage bag which he then puts in a container on the street curb. He joins his wife in bed, but has trouble going to sleep.Next morning, Rachel asks him if he had trouble sleeping because of a hangover and he says yes. Then she asks him if he drove home, after promising to call a cab. He admits that he did, and apologizes. She reminds him that he's a father now, and getting a DUI would jeopardize his career and his ability to provide for his family. Mitch promises to never do it again. He watches as a garbage truck comes and empties the container out front.Mitch takes the couples second car to work that morning. When he gets to the office, he asks the secretary to call around the local hospitals for any information about a man involved in an hit and run around midnight. Mitch is watching the TV news later, at a coffee shop, and learns that police were making a routine traffic stop of a van the night before when they noticed blood dripping from the back doors of the van. They investigated and found the body of Cecil Ackerman, a 24-year old parolee. The driver claimed to have found Ackerman in the road, after being hit by a car, and he was just taking him to a hospital.Mitch hurries over to the police station and speaks with Detective Blake Kanon (Gloria Reuben). He had called her earlier, inquiring about the Ackerman case. She wants to know if the DA assigned the case to him. He tells her it's just a provisional inquiry.Kanon takes Mitch to an area outside an interrogation room, where they look through a window with a mirror on the other side and see Clinton Davis, age 55, a car mechanic with a couple of assault charges on his record. She tells Mitchell that Davis' wife and daughter were murdered in a home invasion a few years back. When Mitchell asks about evidence of a hit-and-run on Ackerman, she says there was none, but they did find Ackerman's blood on Davis' tools and on plastic sheeting in the back of his van. She believes they have enough to charge him with murder, but it's up to the DA's office to decide if they have enough to convict.Kanon also tells Mitch that she ran some key words through data for the Ackerman death, to compare against some unsolved murders, and she found some similarities. Mitch goes to see District Attorney Jones (Philippe Brenninkmeyer) and asks to be assigned to the Ackerman/Davis case. He and Wilson then go to see Davis and Terry Roberts (Dean Harder) of the Public Defenders Office, at the police station. Davis tells Mitch that he didn't do anything, that he's innocent. Mitch tells him he has nothing to worry about in that case. Davis tells them that on the night in question, he left work, went to "group," then drove around. He volunteers to help out at counseling sessions for parolees and he drives around to avoid spending too much time at his home, where the memories of his wife and child are tough to deal with.A parolee named Emmanuel Friar killed Davis' wife and daughter. He was killed the next night attempting to break into someone else's house.In a meeting of the DA and his two assistant DAs, they discuss the case against Davis. The victim was a man previously convicted of child sex abuse. He did two years in jail and had been out on parole for three months. As Wilson itemizes the evidence against Davis, Mitch counters by suggesting how everything could be consistent with a hit-and-run and Davis' attempts to help Ackerman.The DA's secretary (Jessica Burleson) brings in the latest information about the case, including the transcript of Mitch's 911 call. The DA figures the 911 call is potentially damaging to their prosecution of Davis, but if the caller can't be found, then it probably won't work against them. DA Jones tells Mitch and Wilson to charge Davis with first degree murder.At Davis' trial, Mitch is questioning the pathologist who performed the autopsy on Ackerman. Rather than seeking to confirm that the cause of the wounds and Ackerman's death were most likely the tools in Davis' van, Mitch actually emphasizes how the wounds and the oil and grit in those wounds, were consistent with a hit-an-run. Both Blake, sitting in the audience, and Judge Mckenna (John B. Lowe), were surprised at Mitch's statements.Mitch's 911 call is played in court. A female forensic linguistics expert, Dr. Brown (Kelly Wolfman), is on the stand and is somehow able to testify quite accurately about the race, age, and ethnicity of the person making the call. She describes Mitch nearly perfectly. Mitch becomes very nervous when he sees Blake speaking with the linguistic expert outside the courthouse later.Mitch receives a call from a man named Jimmy Logan (Ryan Robbins). Mitch goes to meet Jimmy at a remote location. Turns out that Jimmy is Mitch's step brother and he had just been released from prison. Apparently, Jimmy had burglarized a warehouse that Mitch had been working at, and Mitch was none too happy that his job and his hopes to attend college could have been lost, because he may have been convicted of being an accessory to the crime, given that Jimmy was related to him. Jimmy apologizes for his bad judgment, blaming it on drugs, but he promises he won't ever let Mitch down again. He's looking to reunite with the only family he has. Mitch tells Jimmy that when Rachel helped fill out his application for the DA's office, he told her he had no relatives. So, if he suddenly turns up with a step brother, he has to explain his lie to Rachel and probably to the DA's office.Next day in court, public defender Roberts gets criticized by Judge McKenna for being late. He apologizes and tells the judge that there's been a new development in the case. They found the 911 caller, whose voice was a verified match by Dr. Brown, and he'd been in the courtroom the entire time. Over the strong objections of Mitch, who has been asking the judge for a private conference, Roberts calls Jimmy Logan to the stand. Jimmy testifies that Ackerman was hit by a red SUV.After the charges against Davis are dismissed, Mitch approaches him outside the courthouse, shakes his hand, and wishes him well. Davis asks Mitch what will happen with the hit and run driver. When Mitch says maybe he'll turn himself in, Davis scoffs and says, "would you?"Davis witnesses an argument between a Hispanic man and woman, outside the North Mall, and watches as two security guards escort the man away. Mitch subsequently notices a headline in the Chicago Register newspaper that a man named Pedro Gonzales had been murdered and dumped in the Chicago River. Mitch finds the story on the Internet and listens as a reporter describes how Gonzales' skull had been smashed from behind, perhaps by a hammer. Mitch then accesses the autopsy files and sees that Gonzales also had cuts on his face and arms, consistent with torture. He recalls how Detective Kanon said she'd come up with matches for the way Ackerman died with those of other unsolved murders.Mitch drives back to the site where he hit Ackerman and starts looking around the alleyway. He finds a cigarette butt, same brand as those he'd seen Davis smoking outside the courthouse. He recalls watching Davis flip shut his cigarette lighter, then remembers hearing that same sound coming from the alleyway that night. He continues looking around and finds a bloody hand print on some wood. Now, he's convinced that Davis is probably a murderer. He goes to see Kanon and makes a case based on the similarities of the wounds Ackerman and Gonzales experienced. Kanon really isn't interested and dismisses Mitch out of hand. It's clear she resents that Mitch didn't prosecute Davis as he should have when he had the chance.Mitch stakes out Davis' house and follows him when he leaves. He follows Davis to a building and when Davis goes inside, Mitch does too. Inside, he finds one of the counseling groups that Davis volunteers for. Davis is fixing coffee for the participants. He sees Mitch peeking in the window. Mitch hurries away after he realizes that Davis saw him.That night, Mitch dreams that Davis was standing in his bedroom, holding a hammer, then jolts awake as he dreams that Davis is approaching Ella's crib. The next morning, Mitch goes to the garage and checks to see if his hammer is still on the wall. It's not. He then sees something taped to a bassinette on the shelf. It's one of his business cards, soaked in blood. Obviously, Davis had been in his garage, taken the hammer and left the card, which Mitch must have missed at the scene after he gathered up the others.Mitch next stakes out the police department and when he sees Detective Kanon leaving in her car, he enters the building and finds his way to her office. He starts looking around, eventually accessing her computer and searching for any information about Davis and possible connected cases. He finds a file that shows common themes with the Ackerman murder and several other unsolved murders. He attempts to print out a copy, but the printer doesn't seem to work, so he copies the file onto a thumb drive he had with him.Kanon forgot her cell phone, so she returns to her office. Mitch gets out just before she returns. However, she notices a file in the print queue, and she some paper in and prints it out. She no doubt suspects that Mitch had been in her office.Davis calls Mitch and tells him to stop following him. When Mitch asks Davis why he didn't turn him in, he tells Mitch that he needed a way out from the torture and attempted murder of Ackerman. He had planned to use the bloody business card at the trial as a way to get the murder charge dismissed, and to avoid the double jeopardy of another trial.Mitch tells Davis he won't let him get away with what he's done. Davis tells Mitch that he better, or something might happen to Rachel and Ella after he gets locked up for hit and run.Mitch calls Stuart into an office, where he's got photos of all the murders Kanon had determined had the same modus operandi as Ackerman. He wanted Stuart to help him determine what, if anything, the victims had in common. Stuart asks Mitch to remind him of the details of the deaths of Davis' wife and daughter. Mitch explains that the murderer tied up Davis and forced him to watch as he first tortured, then killed the wife and daughter. He then slit Davis' throat and left him for dead.As Stuart reviews the files on the computer, he mentions how the killer, a man named Emmanuel Friar, was killed during a similar home invasion the subsequent night, that Friar had been recently paroled, blah, blah, blah. Mitch then realizes that the murder victims had all been recent parolees. He speculates that Davis had acted out of the desire to prevent them from committing additional crimes.Mitch calls Jimmy and arranged to meet him at the coffee shop. He wants Jimmy to help him gather proof that Davis is a murderer. He tells Jimmy that if they can get the proof, then he can use the evidence to cut them both a deal with the DA, to get him off the hook for the hit and run and Jimmy off the hook for lying about being the 911 caller.Jimmy doesn't want to risk violating his parole and tells Mitch to let it go. He gets up to leave, but returns and confirms with Mitch that Davis had actually broken into his house. Then he decides to help, telling Mitch, "I may be an asshole, but I'm still your brother."Mitch rents a silver SUV for Jimmy to drive. Jimmy drops Mitch off near Davis' house, then goes to the garage where Davis works and stakes it out. Mitch enters Davis' house through a window and starts looking around. He's not finding anything, except it's clear that Davis probably just eats and sleeps there, nothing more.Davis leaves the garage and gets in his van. Jimmy follows him out to what appears to be a cement plant. He watches as Davis goes inside a warehouse at the plant. Jimmy calls Mitch to see how he's doing. Mitch tells Jimmy that Davis goes to those support group meetings frequently. As he's saying that, it dawns on him that Davis uses those meetings to find his victims. Whomever seems most concerned about committing another crime, that's who Davis would target.When Davis comes back out, he's carrying a small red tool box and disappears from sight. As Mitch is talking to Jimmy, he stumbles on a loose floorboard at Davis' house. He pries up the board and finds a small plastic baggie underneath, containing the parole cards of his murder victims.When Jimmy explains what Davis had been doing up to that point, as soon as he tells Mitch about Davis having a small tool box and disappearing from sight, Mitch yells at Jimmy to get out of there immediately. Right then, Davis appears from behind Jimmy and raises his arm. His hand is holding a hammer. He brings it across his body, smashing the back of Jimmy's head and knocking him unconscious. Jimmy slams against the door of the SUV, leaving a trail of blood. Davis picks him up in a fireman's carry and hauls him inside the warehouse.Mitch realizes something has happened. He drops the parolee cards on the floor and rushes out of the house, yelling to Jimmy that he's coming. He had already determined the cement plant was nearby. Davis picks up the phone and listens briefly, hearing Mitch say that he's coming. Mitch runs as fast as he can across a field to the plant. He sees the SUV and the blood, then hurries over to the door of the warehouse and rushes inside, calling out to Jimmy. He hears Jimmy screaming in pain and he hurries towards the sounds.Davis has placed Jimmy in a chair and tapes his arms down. Jimmy had been tortured and was in bad shape. When Davis hears Mitch shouting for Jimmy, he calmly walks away and returns to his vehicle. He uses Jimmy's cell phone to call 911, imitating a man in suffering, claiming that someone is trying to kill him. He then drops the phone on the ground and drives away.Mitch reaches Jimmy and cuts him loose, then tries to call 911, but he can't get a connection. Mitch carries Jimmie outside, where arriving police draw their weapons and force Mitch to the ground, handcuffing him.Kanon comes to see Mitch in an interrogation room at the jail. He asks her how Jimmy is. She tells him that Jimmy is in a coma, but that the doctors are hopeful. Mitch tells her that he didn't assault Jimmy, that Davis did it. She then pulls out materials from her evidence folder and notes that the weapon used was his hammer, with only his prints on it. Plus, one of his business cards was in the bottom of his toolbox, with Ackerman's blood all over it. Mitch responds by telling Kanon that if he was guilty of Ackerman's death, then why didn't he crucify Davis in court when he had the chance, as he would have been the perfect scapegoat. Mitch then tells Kanon about the baggie in Davis' house, with the parolee ids in it. He has to admit that he broke into Davis' house, so she naturally suspects that maybe he put the baggie there. Mitch decides it's time to stop talking until he has a lawyer present.The jailer comes into the interrogation room with a phone, telling Mitch he has a call from Stuart at the DA's office. However, it's actually Davis calling. Mitch calls Davis and son-of-a-bitch and swears he's going to get him. Davis wonders where all this backbone was when Mitch ran over Ackerman with his SUV, that Ackerman would probably still be alive if he'd waited with him for the ambulance. Of course, that would mean Ackerman would still be running around abusing small children, as he was about to do to a little girl in the woods near the park one day when Davis took him out.Davis tells Mitch that there's now a third option available, one that can help them both get off. He suggests that if another murder with the same M.O. as the others were to occur while Mitch was in custody, then that would take the focus off of him, at the very least creating reasonable doubt as to his guilt. When Davis explains how Mitch doesn't truly understand his pain and emptiness, but that he soon will, Mitch realizes that Davis is talking about killing Rachel and Ella. Mitch starts screaming for the jail guard, who comes in and listens as Mitch shouts that he needs an outside line, that Davis is going to kill his wife. The guard slams Mitch up against the wall in an attempt to subdue him, but Mitch rears back and knocks the guard to the floor, where he strikes his head an goes unconscious. Mitch then grabs his gun and keys and escapes the jail. Outside, he locates the guard's car, evades a couple of other policemen, is recognized by the gate guard who thinks he's just been working late and lets him out, then he heads for home.Davis, meanwhile, rings the doorbell and tells Rachel that he's Detective Kanon. He informs her that Mitch has been charged with murder and he needs to ask her some questions. He then feigns a cough and asks her to get him a glass of water. Rachel sets Ella in her car seat down by the sink, then accidentally knocks some papers onto the floor. Davis is out in the other room, preparing some of his instruments of torture.As she's filling a glass with water, Rachel glances down at the papers on the floor and sees a mug shot of Davis. She knows immediately that he's not a detective and she creeps over to the door and peeks to see what Davis is doing. She grabs Ella and hides in a closet. Back at the jail, Kanon is questioning the jail guard, who tells her what had happened. When Stuart arrives, she asks him if he'd called Mitch earlier. When he says no, Kanon orders another policeman to get a squad car over to Mitch's house immediately. She then rushes out.Davis walks over to the kitchen and sees his mug shot lying on the floor. About then, Ella pushes the key fob of her car, causing the door open/close beep to sound. When Davis rushes to the garage, she exits the closet and locks the garage door. She tries to call 911 on her cell phone, but it doesn't work for some reason, so she hurries back to close Ella in the closet then rushes to the front door to lock it. Davis arrives at the door first, so Rachel turns and runs. She gets out through the patio door at the same time Mitch arrives out front. Rachel stumbles and falls. Davis grabs her and holds a small knife to her throat as Mitch comes out of the house and onto the patio, pointing the gun. Davis orders Mitch to slide the gun over towards him. He makes Rachel pick up the gun and hand it to him. He then points the gun at Mitch as they engage in a back and forth about the need to protect their families and who is more of a man, given all that has happened. Rachel is shaking her head, trying to get Mitch to stop insulting Davis. Davis asks Mitch if he's willing to die to save his family. Mitch doesn't hesitate and says yes. Davis then shoots him in the shoulder and Mitch falls to the ground. Rachel breaks free and rushes over to Mitch. She begs Davis to stop, but Davis tells her to stop begging, that his wife begged and it did no good, that it was a waste of time. Davis grabs Rachel and tells Mitch that he's now going to learn what pain it is he has had to live with.Davis first tells Mitch that he's going to give him an opportunity that he never had, as he tosses the gun down next to Mitch, then dares Mitch to pick it up and prove he could do better than Davis did, and save his family. Davis draws back his arm, preparing to slash Rachel, as Mitch struggles to get to the gun. It looks like Mitch is going to react too slowly, when a shot rings out and Davis goes down. Detective Konan can be seen with her revolver in her hands, having just shot and killed Davis.Some time later, a taxi pulls up at the Brockden house and Jimmy gets out. His face is all bandaged up and he's using a cane. Mitch meets him out on the porch, his own right arm in a sling. Rachel comes out with Ella and they meet Jimmy. Jimmy notes that they'd named Ella after Mitch's mother. They go into the house to get out of the cold.