After a police department baseball game, the whole gang goes to a bar to celebrate McNab's birthday. But, as the waiters bring out the cake, Shawn spots a hooded man by the register with a bulge in his jacket. He runs to warn Lassiter who pulls out his weapons just as the hooded man starts to fire. After a barrage of bullets, the man manages to escape. The cops think it was an attempted robbery but Shawn says the man came there specifically to kill one of them. He believes he will try again, but if they can figure out which one of them was the target, it will give them a clue to the man's identity. The crime scene unit finds a piece of the man's hooded sweatshirt and a motel key in the alley behind the bar. It looks like his pocket ripped as he was fleeing the scene. Lassiter and Juliet head to the motel while Shawn and Gus go back to the bar. While there, Shawn remembers the shooter was wearing an expensive watch, which proves he wasn't a junkie thief. Shawn also realizes that he was deliberately standing in the blind spot of the security cameras. The shooter is much smarter than they give him credit for, which means that the key was planted to lure the cops to the motel. Not only that, but after Shawn recreates the shooting he realizes the target is Lassiter. Shawn calls to warn Lassiter, who is on his way back from finding nothing at the motel. As he leans down to pick up the phone from the floorboard of his car, a shot comes through his windshield, narrowly missing him.
Since Lassiter is now part of the investigation, Vick takes him off the case. So Juliet, Shawn and Gus take his old case files to the Psych office to scour them for a suspect who hates Lassiter enough to want him dead. Juliet is at first distracted by Shawn's new elliptical trainer that looks like it has never been used. She offers to teach him some motivational tricks, but he declines, then names a suspect. Ivan Petrovich, a drug lord Lassiter put away, was just released. Juliet says Petrovich targeted school kids with his drugs, which led high school quarterback Bobby Salamatchia to overdose. They head to the police station to tell Chief Vick about their prime suspect, who it turns out, failed to check in with his parole officer two days ago. Lassiter remembers how smug Petrovich was at his trial because Lassiter was only able to get him on a lesser weapons charge. He also remembers that McNab was there when he busted Petrovich, who swore to get back at them both. McNab is also a target. Juliet rushes to McNab's house to warn him, but his mailbox explodes, injuring him. Vick notices in Petrovich's file that Shawn and Gus are also listed as having worked on the case. Juliet calls Gus, who is fine, but is unable to get a hold of Shawn. Gus hurries over to the Psych office to check on him and finds him on the elliptical machine, pedaling furiously, looking at a note that reads, "If your heart rate drops below 150, you die." Juliet rushes in to help but quickly realizes it's a false alarm when she sees the note. She says she wrote it to motivate Shawn to exercise more. There is no bomb. What's more, if Petrovich knew they were listed in the file, they would already be dead. Shawn and Gus are in the clear.
Lassiter insists on being part of the team that brings in Petrovich. They head to an old front the drug lord once used, and find a secret room in the basement. The lights down there are old and flicker like a strobe, but they see a shadowy image of Petrovich who appears to reach for a gun. Lassiter shoots first, and when the lights finally come on, they see Petrovich dead with two gunshot wounds to his chest.
Now that Petrovich is gone for good, Lassiter says he is going to personally tell the families of those he affected. Shawn watches the news footage of the shooting and notices a scar on Petrovich's hand. Since the shooter in the bar had no scar, Petrovich was not the shooter. Juliet rushes in and tells them that Petrovich died of a massive drug overdose hours before they arrived. Shawn flashes back to the basement and realizes that rats made it look like the dead Petrovich had moved. He asks if there were any signs of restraint on the body, and Juliet confirms there were. Petrovich was forced to overdose, murdered by someone else affected by his crimes - the very people who Lassiter is on his way to visit. They rush out and find him being held at gunpoint by Mr. Salamatchia at Bobby's grave. Salamatchia was angry Petrovich only served a few years time on a gun charge and was already out of jail. He vowed revenge on him and the system that let him down. Shawn is able to distract Salamatchia, which gives Lassiter an opportunity to get the upper hand and disarm the man who had tried to kill them.