With his Jack Reese file spread on the table, Detective Charlie Crews listens to a wiretap recording from Jack Reese's car. "It was six, it is five but it could be just as easily four." Ted walks in, hears it, asks if it's a wiretap, if it's legal, and what it means. Crews indicates that it's not legal, and that he's trying to figure out what it means. Crews gets a call from his partner Detective Dani Reese telling him they've caught a murderer.
In a prison underneath Los Angeles University, a guard lies dead with his throat cut. Charlie notices a tattoo near the victim's ankle with the Greek letters, "Tau, Xi Sigma." Everyone's accounted for in the prison, so they know the killer is still inside. They walk up a stairway and emerge in a gorgeous college campus with equally gorgeous co-eds.
While Crews, Stark and Reese search for the murder weapon, Professor Halliday enters the prison past angry student hecklers. Halliday tells Crews he saw Ryan Sagel, the victim, dead on his computer. He explains that he's conducting a prison experiment with randomly selected students to role-play prisoners and guards. And, that his role is to only observe the experiment as it takes on a life of its own. He's baffled that Ryan was killed, citing strict protocol that bans sharp objects. Reese wonders why it wasn't caught on camera. Halliday says there are 60-second blackouts built in for a heightened effect.
Stark tells Reese they need more people to effectively search for the weapon and guard the kids. Halliday has disappeared and they track him down in the audio/video room, scanning through the footage. Crews kicks him off. Reese calls Tidwell to send more bodies, but three parades has him stretched thin. He says they have two hours to find the killer and then they have to let the kids go. At the station, Tidwell deals with a drunk North Hollywood detective who accidentally discharged his weapon in a bar. The detective, Henry, is crying about his wife leaving him. Henry's partner Det. Karen Davis arrives and asks to talk to Tidwell.
Crews snags Ted to help with the video while Reese tells the students they have to stay put during the investigation. On screen, Crews and Halliday watch the pre-interviews of "inmate" Will, a chemistry major who says that they nicknamed Ryan "Destro." Will, who's in the program for the $83-a-day pay, says he and Destro stayed away from each other. When asked, he doesn't care one way or another about his death. Wayne is next, and he's only worried about still getting credit for the program.
Next is Tate, a cocky "guard" who has completely taken on the persona. Crews asks if Destro bullied him up top for being a poetry major. Full of bravado, Tate says Destro was his brother. Crews sees the same tattoo on his leg that Ryan has. Tate confirms he's a pledge in Ryan's fraternity. Halliday barges in, furious that Tate lied to him about not knowing Ryan beforehand. He accuses him of killing Ryan. Tate responds by chanting about "us and them." Crews clamps his hand over Tate's mouth to avoid a prison riot. Too late, the students riot, calling for a terrified Halliday who hides behind a door.
In the hallway, Crews sees the "guards" are keeping the chanting "prisoners" at bay. However, there's been a prison break. One of the "inmate" students, Janis, is missing. The riot ends and Crews, Reese, Bobby and the "guards" lock the prisoners in their cells as Halliday watches. Halliday thinks Tate is the killer and wants to question him, but Crews shuts him down. He then makes Bobby the warden and strips Halliday of the title.
In Janis' dorm room, Crews talks to her roommate Glenda, who hasn't seen Janis for five days. He learns that Janis is the school's moose mascot. He asks Glenda what the "BW" means on Janis's calendar, but she doesn't know. Crews peeks at Janis's open email and sees it stands for Ben Wise. Glenda tells him where Ben lives, across campus at home. Crews wonders how she got there without being seen. Off Crews's tip, Reese pulls up outside Ben's parents' house to see Janis, in costume, screaming at a cheerleader as the two-timing Ben stands by. Janis chucks the moose head at Ben.
At the station, while Henry sleeps on the couch in Tidwell's office, Tidwell talks to Davis. She wants Tidwell to charge him, but he is reluctant, saying the job can get to you. Davis says it's always something with Henry. Tidwell asks, "Like what?" Davis looks into Tidwell's office, where Henry is no longer sleeping, but sitting on the desk, crying and clutching a gun. "Like that," Davis says.
Back at the prison, Ted scans through the audio and video. Bobby advises him to look for any arguments or conflicts. Tate talks to Bobby about how the experiment has taught him the importance of the police. He says he's thinking about trying out for the LAPD.
Crews and Reese both lean towards Tate as a suspect since he lied about knowing Destro. They go to Tau Xi Sig where the partying frat boys are reluctant to talk, because the police helped get their charter suspended. They point at Crews and Reese and chant, "There's us and there's them!" Crews intimidates a student into talking, and he says Tate isn't in their fraternity. Back at the prison, the pizza-fed students are jovial. All except Tate, who knows by Crews' look that his gig is up.
Charlie gets a call from Jennifer, his ex-wife. He apologizes for asking her husband if he could sleep with her. She tells him she got a call from a reporter who wanted to talk about his time in prison. Crews is visibly shaken. Jennifer says the reporter wanted to know if while he was in prison, Crews sent a lawyer away who wanted to prove his innocence. She asks him if that's true. He doesn't answer. When asked what she said, Jennifer says she told the reporter to go to hell.
Crews and Reese go to work on Tate. Crews calls him on being a weakling who follows the strong. First, for wanting to be in Destro's frat and second, for wanting to be in the LAPD because Stark held the keys. He throws a wet paper towel at him, tells him he knows what to do. Tate sadly wipes the drawn-on Tau Xi Sig tattoo from his leg. Crews asks him if Destro laughed at him for the fake tattoo. Tate said he never showed it to him, because like Crews said, he's weak.
In the A/V room, Ted shows Crews, Reese and Halliday video of Ryan accusing Perry, an inmate, of sneaking junk food contraband into the prison. Perry denies it but Ryan says he's going in the Hole for two days. Perry freaks as he's dragged toward the Hole, an empty piano crate. Will steps in and cops to it, saving claustrophobic Perry from the punishment. Halliday admits he planted the contraband to heighten the dynamic, but there was nothing sharp in it. Reese wonders why Perry would go in the Hole for something he didn't do.
At the police station, Tidwell and Davis try to coax the gun away from Henry, who is holding it to his head. They try to relate to his pain. Davis says that Tidwell, who equates women with viral infections, took the job she'd worked her entire life for, and it hurt. Tidwell says he's been there after his wife left him, and that Tullamore Dew, the Afghan Whigs, and lots of strippers helped to dull it. Henry goes ballistic, and Davis pulls him aside to tell Tidwell that Henry's wife is a stripper. Whoops.
Crews and Reese ask Will why he went to the Hole for something he didn't do. Crews, who sees the psychological torture at work, says he went because it's safe. Next, they talk to Perry, who is unaffected and thinks it's just an awesome game. They ask if he told the guards he was claustrophobic. He didn't. Next they question Janis, who says Destro had his frat friends take Ben out and hook him up with the cheerleader. Destro showed her the photos on his phone; according to her, not knowing he was Janis's boyfriend. She said it was her "worst nightmare." Crews and Reese notice that a lot of "worst nightmares" are happening to the inmates and wonder if it's more than just coincidence.
In the hallway, Crews finds the murder weapon in the "exit" sign, having smelled it melting on the bulbs. Crews, Reese and Bobby examine it - it's melted plastic that's been scraped to a point. They line the students up and inspect their hands. Reese stops before a nervous guard and sees her yellow fingers. Crews asks her to show them where she smoked, and she takes them to her stashed cigarettes and lighter. She says Will saw her smoking, but despite the torture the guards put him through, he didn't tell on her. She says they singled Will out because Destro told them Halliday wanted him broken. If they broke Will, then they would win. She says they did terrible things to him, and it wasn't on video because they did it during blackouts.
At the police station, Tidwell and Davis are still trying to talk Henry into giving up the gun. To Davis's shock, Tidwell tells Henry to "just do it." He tough talks Henry, telling him to pull the trigger and he'll call the cleaning crew, or to get the hell out of his office. It works. Henry lowers the gun, says, "She was the best thing that ever happened to me." Tidwell says, "No. She wasn't. She was the first." Later, Tidwell reveals to Davis that the gun was empty, and he let him go on because sometimes a guy's gotta talk.
Ted tells Crews and Reese that from the video, he can tell where some of the students were during the blackout when the murder took place. He says Will, who was in the Hole, couldn't have done it. In the interrogation cell, Crews and Reese question Halliday about his instructions to Destro regarding Will. Halliday denies it, saying he was just an observer. Crews calls Jennifer and tells her he traced the reporter's number and texted it to her. He asks her to call it. Halliday's phone rings. Busted. Infuriated, Crews says Halliday knew who he was and called his wife. He accuses him of not just being an observer, but of trying to keep him from doing his job.
As Reese follows, Crews shoves Halliday into the A/V room where Ted sits in front of the monitors. Crews asks Halliday why he keeps trying to get at the computer. Halliday asks for a university representative. Reese leaves, closes the door. Time for Halliday's worst nightmare. Ted and Crews intimidate him, prison style. Ted says since Halliday knows Charlie's case, he knows a guard got killed and that they still don't know who did it. He says that sometimes things never get solved. Halliday buckles and shows them a video where Destro, having taken over the prison, has him by the throat. Destro says that Halliday gave him the students' personal files and told him to use their fears against them. He slaps Halliday, and then screams at him to get out of "his" prison. Halliday flees.
Reese tells Halliday that he created Destro, and then like a coward left the kids alone with him. Halliday says the door was never locked, that everyone just fell into their roles. He says you don't need locks for a prison. Just prisoners. It's repulsive to Crews, who knows the prison mentality all too well. He has Stark arrest a stunned Halliday on incitement of gross bodily harm. Crews notes that it's seven years for each count: 20 students adds up to 140 years. They perp walk Halliday in front of his student guinea pigs. Afterward, Bobby asks Crews and Reese, "Who exactly is the killer?"
Crews and Reese deduce that if nothing was locked, Will could have left the Hole during blackout. They wonder where he got the plastic, and then realize he wanted to be in the Hole for a reason. The review the video with Ted. On screen, Tate and Michelle approach the Hole, passing a table with the contraband on it and a plastic bag. After a blackout, the bag is gone. Still watching the video, the lights go out again. When they come back on, Destro is dead on the floor.
Reese, Crews and Ted figure that Will left the Hole during a blackout and no one would know he was gone. Then, he made the shank by melting the plastic bag. Later, in a real prison cell, Crews sits with Will. Crews tells him the first three years will be the hardest. Then he adds, "Just because you're in there, you don't have to be in there. You can go somewhere else."
In his mansion, Crews looks at clippings, files and photos from the Jack Reese file. He's going over the recording again.