Lassiter and Juliet are at the scene of a possible suicide with Gus, Shawn and Abigail. It appears the victim hung himself, but Shawn sees signs of murder and discovers dog tags stuffed down the dead man's throat. This is not just a murder now, it's a military crime, which poses jurisdictional problems. But Juliet says she knows someone who might be able to help with that, and she calls her brother Ewan, an ex-military man who is now hired out by the government for covert missions. He is in the middle of finishing up a job, but he is able to tell Juliet that swallowing dog tags is a sign of shame. He then tells her he's near Santa Barbara and is coming in for a visit.
The next day, Ewan is at the police station meeting the gang when the autopsy report comes in, supporting the murder theory. They will now need to go to the base and ask questions. Juliet thinks Ewan could be of assistance and asks him to come along. At the gate to the base, he flashes his credentials and they are immediately admitted. There, they meet Major General Felts, who tells them that Starks' death is a military matter. But Lassiter and Juliet insist on seeing Stark's belongings and tracing his movements that day. Felts acquiesces and tells his assistant Lt. Wallach to take them to Starks' barracks and to the motor pool where he worked. The group decides to split up, and Ewan goes with Shawn and Gus to the motor pool where Shawn discovers that Starks signed out of work on Monday. A private there tells them it could be because he was either sick, injured or had a meeting with a superior. Just then, Ewan gets a call from his boss, who knows where he is and what he's doing. He tells Ewan to root out the bad seed on the base and cover it up. When Ewan hangs up, another private hands him a file on Starks. Ewan rips out the page where it says Starks was meeting with Felts on Monday and shreds it.
The next day at the police station, Lassiter and Juliet say they found nothing in their search through Starks' belongings. Ewan says he's sorry the file didn't turn up anything more, either. He then says he thinks it might have been a suicide all along and unfortunately can't get them back on the base again. Shawn looks at the file and notices a page has been torn out. He wonders at Ewan's sudden lack of desire to help and suspects Ewan might somehow be involved. Shawn and Gus decide to sneak back onto the base themselves, but are caught and brought to Felts. Felts warns them not to try that again, then as a Private Templeton uncuffs them, he tells them he knows something about Starks' death and asks to meet up with them later. As the guys leave, they see Ewan talking to a soldier. His back is to them, so he doesn't notice they are there. They leave to wait for Templeton at the meet, but he doesn't show up. Instead, Felts and Wallach find him floating in the pool, dead. Felts wonders how a trained soldier could drown like that and knows the cops will have questions.
At the police station the next morning, Shawn and Gus let Lassiter in on their suspicions of Ewan. Juliet overhears and is irate. Felts comes to the station as a courtesy, but shuts down when Lassiter turns the conversation into an interrogation. Shawn suggests to Juliet that they get Ewan to help them get back on the base, that way they can tell which side he's really on. Ewan, then, takes Shawn, Gus and Juliet to the weapons depot at the base, where Templeton worked. There they learn that Starks sometimes substituted for Templeton when Templeton wanted to sneak off to meet his girlfriend. Starks must have seen something suspicious while working there. Ewan, then, gets another call from his boss. Ewan tells him that Shawn is too good to slow down, so he will now let the psychic lead him to the target and take care of it from there.
That night, Shawn, Ewan and Gus stake out the weapons depot and sneak onto the back of a truck as it pulls out. The truck stops at a remote air strip where they catch Wallach selling weapons on the side. This is what Starks must have stumbled across when he filled in for Templeton. He was going to tell Felts but Wallach killed them both to cover his tracks. Wallach spots them and takes off. The buyers shower the guys with a hail of bullets but Ewan is able to get them all out alive. Back at the base, Felts says he will track the stolen weapons and set up a manhunt for Wallach. Ewan tells them he's got another assignment and is unable to help with the search. He then leaves but Shawn remembers that he had been working against them for a while. Suspicious, Shawn and Gus follow Ewan to a pier where he has Wallach tied up, with a gun trained on him. Ewan is about to complete his mission and clean up the situation. He tells Shawn and Gus to leave for their own good, but Juliet and Lassiter arrive and are forced to arrest Ewan. Later, as Juliet and Lassiter wait to meet Ewan as he is transferred to a different prison, they learn he is mysteriously no longer in custody. Meanwhile, Shawn and Gus are at the airport, saying goodbye to Abigail who is moving to Africa to teach, leaving her relationship with Shawn up in the air.