A man with a gun tells a boy to get under the bed. The man looks outside, hears a noise behind him, and fires -- just missing the boy. A woman enters and says, "You need help." The man slumps against a wall.
Cal and Gillian are called to a military base, where Colonel Powler tells them that the man, Sgt. Jeff Turley, returned from Iraq six months ago. He's due to receive a Silver Star for bravery, but he's currently in restraints for nearly killing his son, Jake, with a weapon he's not authorized to have. Cal suspects Post-Traumatic Stress Disorder (PTSD) and asks Turley who is trying to kill him. Turley doesn't know. He also denies having PTSD.
Back at the Lightman Group office, Gillian tells Ria that Turley hasn't been tested for PTSD because there's a six-month backlog. Cal asks Powler to expedite matters so Turley can undergo FMRI testing, which Gillian explains to Turley's wife, Becky, involves showing him pictures and recording his brain activity.
When tested, Turley has the same reaction to photos of angry faces as he does to neutral faces. Basically, everyone is the enemy. And that's PTSD -- which doesn't mean someone doesn't want him dead. But when Cal asks why he's getting a Silver Star, Turley refuses to talk about it. Cal says they need to get to the root of Turley's problem.
Gillian explains to Ria that Turley's not lying, but his brain is lying to him. His only memories are nightmares or flashbacks, but by re-traumatizing Turley in a controlled environment, they can re-integrate his memories.
So they hook up Turley to what's basically a giant video game, where as Turley describes the action, Eli makes it happen on-screen. Turley's driving the second Humvee in a convoy with Sgt. Ronnie Baca beside him when the first Humvee hits an IED. As bullets rain down on Turley's Humvee, his gunner is killed, and he's ordered to dismount and enter a red door. But he doesn't move. When Cal calls Turley a coward, he calls him "Captain." Now Cal wants to question Turley's captain.
Gillian and Ria go to the base, where Captain Renshaw says Turley froze, and if he hadn't pulled him from the Humvee seconds before it exploded, Turley would be dead. When Gillian asks why Turley was recommended for a Silver Star, Renshaw explains that bravery is overcoming fear, which Turley did. Renshaw will give them the after-action report. Gillian says the pride in his voice indicates he's hiding something. Meanwhile, Cal is at home looking through old photos of his father as a soldier.
After reading the report, Cal doesn't buy it. Then Cal questions Jake and discovers he has severe bruises, which Jake says came from his dad trying to protect him from Ronnie -- that is, Sgt. Ronnie Baca -- who lives above their garage now. Jake also says that he saw Ronnie and Becky being affectionate. Becky denies this, saying when her husband grabs a knife and vanishes, Ronnie is the only person who can handle him. Eli interrupts: Turley's disappeared. Becky tells Jake to get Ronnie.
Cal and Gillian question Ronnie, who admits hitting Jake, denies sleeping with Becky, and says Turley usually goes to a local veterans cemetery. When Cal asks about the red door, Ronnie says to ask Turley or Renshaw. Gillian knows Ronnie's hiding something else. What? His gun is missing.
Cal and Gillian go to Renshaw's home and tell him that Turley is loose with a gun. Renshaw says he hasn't seen Turley. But as Cal and Gillian are leaving, they see Turley's been holding a gun on Renshaw the whole time. Gillian knocks again and gets Renshaw to let her in, while Cal enters through a side door, takes Renshaw's pistol from a drawer, and uses this to persuade Turley to give up his gun.
They return to the office and put Turley back in the simulated environment video game. When Turley screams his son is behind the red door, Cal orders him to kick it down or he'll be raising his son from a loony bin. "React to contact, it's what we train for," says Turley, who visualizes killing an armed 10 year old. Cal says this isn't true, but they can't tell Turley that.
So they return to the base, where Cal and Gillian have Renshaw, Turley, and Ronnie re-enact the event. When Turley froze, Renshaw panicked and accidentally killed a fellow soldier -- which he kept out of the report -- then called in an air strike to cover it up. A lot of people died from that air strike, and that's what Turley, who felt responsible, couldn't handle. Although friendly fire is not a crime, covering it up is, and Renshaw gets handcuffed.
Cal, Gillian, and the Turleys go to the veterans cemetery, where Turley places flowers on the grave of the soldier who was killed by friendly fire. Cal tells Turley that he saved Ronnie's life, got the Silver Star he deserved, and honored the victim, so get a good night's sleep. The family hugs.
Cal returns to the office and puts himself through a series of FMRI scans, which he then shows Emily, explaining her picture stimulates feelings of love, Zoe inspires flight, and Gillian's does fireworks. Then he shows her a picture of his soldier father. This is news to Emily. Cal says he never asked him about the war, after which his dad went back to rail-yard work. Emily says she'd like to meet him. "Yeah, well, one day," Cal sighs.