Zach Evans is at home and has tied his new wife Amanda to a chair. He sharpens a knife and says that he's ready, and tells Amanda that he's going to kill her because she rejected him. Amanda insists that she doesn't know who he is and Zach wonders why she doesn't recognize him after so long. She continues to deny that Zach is her husband and Zach's eyes briefly turn silver before he brings the knife down into Amanda's body.
Dean is driving down the road in the Impala while Sam sleeps next to him. Sam is dreaming of a yellow-eyed man visiting him when he was young, and then being chased by zombies, and then his mother Mary suspended from the ceiling, burning. He wakes up from his nightmare and Dean reminds him that they're on their way to Missouri to check out a story about Zach Evans killing his wife, Amanda. There have been four other murders in the same town and in each case, the killers denied murdering anyone. Sam figures that it's a normal series of murders and nothing to do with their hunting, but Dean points out that each suspect had an ironclad alibi for the time of the murder. He's eager to check it out and points out that if John were there, he'd be doing the same thing. Sam would but Sam would rather be out hunting for their missing father but finally gives in to his older brother's wishes.
The brothers arrive in town and visit the local police station, posing as Federal marshals. Dean notices an attractive female officer and asks her where they can find the investigating officer, Katherine Boyle. The woman says that she's Katherine and takes them to see Zach. Zach tells the Winchesters that he was visiting his brother and found Amanda dead when he returned home. He insists that he's innocent, but Katherine provides video footage showing Zach going into his house just before the murder. Sam is convinced that Zach is innocent but Dean isn't so sure. They rewind the tape and Sam points out that the killer's eyes briefly glowed silver. He reminds Dean that John told them that spirits glow on camera and suggests that a doppelganger is responsible for the murders.
Katherine accompanies Sam and Dean to the Evans house and Dean starts flirting with the police officer. She cuts her finger on the door frame and Dean quickly bandages it, saying that she should have a drink with him because he saved her life. Katherine is not impressed. Sam calls them in and they secretly check for any spirit presence. Meanwhile, Katherine finds a photo and starts crying, and Dean realizes that the two women in the photo are Katherine and Amanda years ago. She explains that they were friends for years and Dean offers his condolences. Meanwhile, Sam gets a window open and finds a trail of blood leading down the side of the house and into a nearby sewer grate. Realizing that it's significant, Sam quickly gets Dean out, loudly saying that there's nothing there so that Katherine hears him.
Later, the brothers go into the sewers armed with rock salt ammunition. As they make their way through the tunnels, the creature wearing Zach's shape attacks them, injuring Dean's shoulder and knocking him out. It leaps to the ceiling with superhuman agility, ducks out of the light, and then returns to attack Sam and knock him out as well.
Later, Sam wakes up and finds himself suspended from a pillar above a deep vertical shaft. "Dean" is standing nearby, unharmed, but Sam realizes that he's the shapeshifter. It pretends that it's still Dean and acts offended that Sam doesn't believe him. It's able to read Sam's mind and sees his dreams, and says that it knows about Dean's suffering because it's seen the older Winchester's memories. It tells Sam about how Dean was stuck on the road hunting monsters while Sam was enjoying college. Then John disappeared and Dean was betrayed again. The shapeshifter tells Sam that it's going to enjoy itself with Katherine and walks out.
Struggling to free himself, Sam knocks loose a few bricks. They fall down the shaft and hit Dean, who is tied up on a lower level. Dean wakes up and Sam tells him what is happening. As they try to work out what kind of monster they're facing, Dean gets his cigarette lighter and burn through his ropes.
Further in the tunnels, the shapeshifter destroys its Dean "skin," regaining its original form.
Dean manages to burn through his ropes and climbs up the shaft, using a chain to swing over to the ledge. He frees Sam and they drive to Katherine's apartment before the shapeshifter can kill her. As Dean drives, Sam checks their father's journal and finds an entry saying that silver can kill shapeshifters. The brothers burst in and split up to search the house. Dean finds Katherine and she says that she's fine. When he tells Katherine that a shapeshifter is after her, she draws a gun on him and says that she checked and confirmed that Sam and Dean aren't marshals. As he tries to convince her that he's sincere, Dean notices that "Katherine" doesn't have the cut that he bandaged earlier and realizes that she's the shapeshifter. He grabs some dirt from a potted plant and throws it in the creature's face, then takes its gun and turns it on it the monster. Before he can shoot, the police arrive and surround the apartment. They call on Dean to surrender, and the shapeshifter leaps up through the skylight and runs away.
Outside, Sam sees the cars and tries to get close to the apartment. A SWAT officer captures him but then removes his mask, revealing that he's Dean. Upstairs, the other officers find the SWAT officer tied up and missing his uniform.
The brothers drive off, trying to work out where the shapeshifter hid Katherine. They figure the creature stashed her in the sewers, and Dean tells Sam to head for the nearest sewer line. However, Dean then draws his gun and accuses Sam of being the shapeshifter. Sam denies it and figures that the shapeshifter is pretending to be Dean. They struggle for the gun and Dean slams down on the brakes, knocking the gun to the floor. Sam manages to grab the gun and prepares to shoot Dean... only for the real Sam to step out onto the road ahead. He braces himself and then shoots, killing the shapeshifter. Dean grabs the wheel and brakes the Impala to a halt just in time.
Later, Sam and Dean search the sewer line and find Katherine. Dean helps her out and says that he's just doing his job as part of the family business. They drop Katherine off at a gas station and say their goodbyes, and Katherine assures them that she'll get the suspects cleared and released. Sam and Dean wish her well and drive off.
Written by Gadfly on May 22, 2016